function sum(x, y) {
if (y !== undefined) {
return x + y;
} else {
return function(y) { return x + y; };
}
}
Output
console.log(sum(2,3)); // Outputs 5
console.log(sum(2)(3)); // Outputs 5
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-type" content="text/html;charset=UTF-8">
<title>Show File Data</title>
<script type='text/javascript'>
function showFileSize() {
var input, file, extension;
// (Can't use `typeof FileReader === "function"` because apparently
// it comes back as "object" on some browsers. So just see if it's there
// at all.)
if (!window.FileReader) {
bodyAppend("p", "The file API isn't supported on this browser yet.");
return;
}
input = document.getElementById('fileinput');
if (!input) {
bodyAppend("p", "Um, couldn't find the fileinput element.");
} else if (!input.files) {
bodyAppend("p", "This browser doesn't seem to support the `files` property of file inputs.");
} else if (!input.files[0]) {
bodyAppend("p", "Please select a file before clicking 'Load'");
} else {
file = input.files[0];
extension = file.name.substring(file.name.lastIndexOf('.') + 1);
bodyAppend("p", "File Name: " + file.name + "<br/>File Size: " + file.size + " bytes <br/>File Extension: " + extension);
}
}
function bodyAppend(tagName, innerHTML) {
var elm;
elm = document.createElement(tagName);
elm.innerHTML = innerHTML;
document.body.appendChild(elm);
}
</script>
</head>
<body>
<form action='#' onsubmit="return false;">
<input type='file' id='fileinput'>
<input type='button' id='btnLoad' value='Load' onclick='showFileSize();'>
</form>
</body>
</html>
<!DOCTYPE html>
<html>
<head>
<title>JavaScript Captcha Example</title>
</head>
<script>
var captcha;
function generateCaptcha() {
var a = Math.floor((Math.random() * 10));
var b = Math.floor((Math.random() * 10));
var c = Math.floor((Math.random() * 10));
var d = Math.floor((Math.random() * 10));
captcha = a.toString() + b.toString() + c.toString() + d.toString();
document.getElementById("captcha").value = captcha;
}
function check() {
var input=document.getElementById("inputText").value;
if(input == captcha) {
alert("Valid Captcha");
} else {
alert("Invalid Captcha");
}
}
</script>
<body onload="generateCaptcha()">
<input type="text" id="captcha" disabled/><br/><br/>
<input type="text" id="inputText"/><br/><br/>
<button onclick="generateCaptcha()">Refresh</button>
<button onclick="check()">Submit</button>
</body>
</html>
<!DOCTYPE html>
<html>
<head>
<title>Stopwatch Example</title>
</head>
<body>
<form action="" method="post">
<h4>Simple stopwatch made in JavaScript</h4>
<input type="button" onclick="startWatch()" value="START" />
<input type="button" onclick="stopWatch()" value="STOP" />
<input type="button" onclick="resetWatch()" value="ZERO" />
</form>
<p id="res"><span id="min">0</span> : <span id="sec">00</span> : <span id="msec">000</span></p>
<p>In this example Date() methods co-operate with timing function setInterval().</p>
<script type="text/javascript">
var timer = null;
var min_txt = document.getElementById("min");
var min = Number(min_txt.innerHTML);
var sec_txt = document.getElementById("sec");
var sec = Number(sec_txt.innerHTML);
var msec_txt = document.getElementById("msec");
var msec = Number(msec_txt.innerHTML);
function stopTimeMilliseconds(timer) {
if (timer) {
clearInterval(timer);
return timer;
}
else return timer;
}
function startTimeMilliseconds() {
var currDate = new Date();
return currDate.getTime();
}
function getElapsedTimeMilliseconds(startMilliseconds) {
if (startMilliseconds > 0) {
var currDate = new Date();
elapsedMilliseconds = (currDate.getTime() - startMilliseconds);
return elapsedMilliseconds;
} else {
return elapsedMilliseconds = 0;
}
}
function startWatch() {
// START TIMER
timer = stopTimeMilliseconds(timer);
var startMilliseconds = startTimeMilliseconds();
timer = setInterval(function() {
var elapsedMilliseconds = getElapsedTimeMilliseconds(startMilliseconds);
if (msec < 10) {
msec_txt.innerHTML = "00" + msec;
} else if (msec < 100) {
msec_txt.innerHTML = "0" + msec;
} else {
msec_txt.innerHTML = msec;
}
if (sec < 10) {
sec_txt.innerHTML = "0" + sec;
} else {
sec_txt.innerHTML = sec;
}
min_txt.innerHTML = min;
msec = elapsedMilliseconds;
if (min >= 59 && sec >=59 && msec > 900) {
timer = stopTimeMilliseconds(timer);
return true;
}
if (sec > 59) {
sec = 0;
min++;
}
if (msec > 999) {
msec = 0;
sec++;
startWatch();
}
}, 10);
}
function stopWatch() {
// STOP TIMER
timer = stopTimeMilliseconds(timer);
return true;
}
function resetWatch() {
// REZERO TIMER
timer = stopTimeMilliseconds(timer);
msec_txt.innerHTML = "000";
msec = 0;
sec_txt.innerHTML = "00";
sec = 0;
min_txt.innerHTML = "0";
min = 0;
return true;
}
</script>
</body>
</html>
function reverseString(str){
let stringRev ="";
for(let i = str.length; i >= 0; i--) {
stringRev = stringRev + str.charAt(i);
}
return stringRev;
}
alert(reverseString("Pradeep")); // Output: peedarP
function isEmpty(obj) {
return Object.keys(obj).length === 0;
}
var pattern = /^\w+@[a-zA-Z_]+?\.[a-zA-Z]{2,3}$/;
var newPassword = "Pq5*@a{J";
var regularExpression = new RegExp("^(?=.*[a-z])(?=.*[A-Z])(?=.*[0-9])(?=.*[!@#\$%\^&\*])(?=.{8,})");
if(!regularExpression.test(newPassword)) {
alert("Password should contain atleast one number and one special character !");
}
| RegEx | Description |
|---|---|
| ^ | The password string will start this way |
| (?=.*[a-z]) | The string must contain at least 1 lowercase alphabetical character |
| (?=.*[A-Z]) | The string must contain at least 1 uppercase alphabetical character |
| (?=.*[0-9]) | The string must contain at least 1 numeric character |
| (?=.[!@#$%\^&]) | The string must contain at least one special character, but we are escaping reserved RegEx characters to avoid conflict |
| (?=.{8,}) | The string must be eight characters or longer |
Example 01:
const matches = (obj, source) =>
Object.keys(source).every(key => obj.hasOwnProperty(key) && obj[key] === source[key]);
console.log(matches({ age: 25, hair: 'long', beard: true }, { hair: 'long', beard: true })); // true
console.log(matches({ hair: 'long', beard: true }, { age: 25, hair: 'long', beard: true })); // false
console.log(matches({ hair: 'long', beard: true }, { age: 26, hair: 'long', beard: true })); // false
Example 02:
const k1 = {fruit: '🥝'};
const k2 = {fruit: '🥝'};
// Using JavaScript
JSON.stringify(k1) === JSON.stringify(k2); // true
Example 03:
const one = {
fruit: '🥝',
energy: '255kJ',
};
const two = {
energy: '255kJ',
fruit: '🥝',
};
// Using JavaScript
JSON.stringify(one) === JSON.stringify(two); // false
var myArray = [
{field: 'id', operator: 'eq'},
{field: 'cStatus', operator: 'eq'},
{field: 'money', operator: 'eq'}
];
myArray = myArray.filter(function( obj ) {
return obj.field !== 'money';
});
Console.log(myArray);
Output
myArray = [
{field: "id", operator: "eq"}
{field: "cStatus", operator: "eq"}
]
console.log(+'meow'); // Output: NaN
var result;
for (var i = 5; i > 0; i--) {
result = result + i;
}
console.log(result); // Output: NaN
var a = 1.2;
console.log(typeof a); // Output: Number
var x = 10;
if (x) {
let x = 4;
}
console.log(x); // Output: 10
console.log(0.1 + 0.2 == 0.3); // Output: false
console.log(1 + -'1' + 2); // Output: 2
(function(x) {
return (function(y) {
console.log(x);
})(10);
})(20); // Output: 20
var num = 20;
var getNumber = function() {
console.log(num);
var num = 10;
};
getNumber(); // Output: undefined
function f1() {
num = 10;
}
f1();
console.log('window.num: '+window.num); // output: 10
console.log('(null + undefined): '+(null + undefined)); // Output: NaN
(function() {
var a = (b = 3);
})();
console.log('value of a : ' + a); // Output: undefined
console.log('value of b : ' + b); // Output: 3
var y = 1;
if (function f() {}) {
y += typeof f;
}
console.log(y); // Output: 1Object
var k = 1;
if (1) {
eval(function foo() {});
k += typeof foo;
}
console.log(k); // Output: 1undefined
var k = 1;
if (1) {
function foo() {}
k += typeof foo;
}
console.log(k); // Output: 1function
console.log('(-1 / 0): '+(-1 / 0)); // Output: -Infinity
console.log('(1 / 0): '+(1 / 0)); // Output: Infinity
console.log('(0 / 0): '+(0 / 0)); // Output: NaN
console.log('(0 / 1): '+(0 / 1)); // Output: 0
var a = 4;
var b = '5';
var c = 6;
console.log('(a + b): '+(a + b)); // Output: 45
console.log('(a - b): '+(a - b)); // Output: -1
console.log('(a * b): '+(a * b)); // Output: 20
console.log('(a / b): '+(a / b)); // Output: 0.8
console.log('(a % b): '+(a % b)); // Output: 4
console.log("MAX : " + Math.max(10, 2, NaN)); // Output: NaN
console.log("MAX : " + Math.max()); // Output: -Infinity
(function(){
var a = b = 3;
})();
console.log("a defined? " + (typeof a !== 'undefined')); // Output: true
console.log("b defined? " + (typeof b !== 'undefined')); // Output: true
var myObject = {
foo: "bar",
func: function() {
var self = this;
console.log("outer func: this.foo = " + this.foo); // Output: this.foo = bar
console.log("outer func: self.foo = " + self.foo); // Output: self.foo = bar
(function() {
console.log("inner func: this.foo = " + this.foo); // Output: this.foo = function foo() {}
console.log("inner func: self.foo = " + self.foo); // Output: self.foo = bar
}());
}
};
myObject.func();
console.log(0.1 + 0.2); // Output: 0.30000000000000004
console.log(0.1 + 0.2 == 0.3); // Output: false
(function() {
console.log(1);
setTimeout(function(){console.log(2)}, 1000);
setTimeout(function(){console.log(3)}, 0);
console.log(4);
})();
// Output: 1, 4, 3, 2
var arr1 = "john".split('');
var arr2 = arr1.reverse();
var arr3 = "jones".split('');
arr2.push(arr3);
console.log("array 1: length=" + arr1.length + " last=" + arr1.slice(-1)); //array 1: length=5 last=j,o,n,e,s
console.log("array 2: length=" + arr2.length + " last=" + arr2.slice(-1)); //array 2: length=5 last=j,o,n,e,s
console.log(1 + "2" + "2"); // Output: 122
console.log(1 + +"2" + "2"); // Output: 32
console.log(1 + -"1" + "2"); // Output: 02
console.log(+"1" + "1" + "2"); // Output: 112
console.log( "A" - "B" + "2"); // Output: NaN2
console.log( "A" - "B" + 2); // Output: NaN
for (var i = 0; i < 5; i++) {
setTimeout(function() { console.log(i); }, i * 1000 );
}
// Output: 145, 5, 5, 5, 5, 5
for (var i = 0; i < 5; i++) {
(function(x) {
setTimeout(function() { console.log(x); }, x * 1000 );
})(i);
}
//Output:- 0, 1, 2, 3, 4
console.log("0 || 1 = "+(0 || 1)); // Output: 1
console.log("1 || 2 = "+(1 || 2)); // Output: 1
console.log("0 && 1 = "+(0 && 1)); // Output: 0
console.log("1 && 2 = "+(1 && 2)); // Output: 2
console.log(false == '0') // Output: true
console.log(false === '0') // Output: false
var a={},
b={key:'b'},
c={key:'c'};
a[b]=123;
a[c]=456;
console.log(a[b]); // Output: 456
console.log((function f(n){return ((n > 1) ? n * f(n-1) : n)})(10)); // Output: 3628800
(function(x) {
return (function(y) {
console.log(x); //1
})(2)
})(1);
var hero = {
_name: 'John Doe',
getSecretIdentity: function (){
return this._name;
}
};
var stoleSecretIdentity = hero.getSecretIdentity;
console.log(stoleSecretIdentity()); // Output: undefined
console.log(hero.getSecretIdentity()); // Output: John Doe
var length = 10;
function fn() {
console.log(this.length);
}
var obj = {
length: 5,
method: function(fn) {
fn();
arguments[0]();
}
};
obj.method(fn, 1);
//Output: 10, 2
(function () {
try {
throw new Error();
} catch (x) {
var x = 1, y = 2;
console.log(x);
}
console.log(x);
console.log(y);
})();
//Output: 1, undefined, 2
var x = 21;
var girl = function () {
console.log(x); // Output: undefined
var x = 20;
};
girl ();
console.log(1 < 2 < 3); // Output: true
console.log(3 > 2 > 1); // Output: false
console.log(typeof typeof 1); // Output: string
var b = 1;
function outer(){
var b = 2
function inner(){
b++;
var b = 3;
console.log(b) //3
}
inner();
}
outer();
x = 10
console.log(x);
var x; // Output: 10
const arr = [1, 2];
arr.push(3); // Output: 1, 2, 3
var o = new F();
o.constructor === F;
let sum = (a, b) => { a + b;};
console.log(sum(10, 20)); // Output: undefined; return keyword is missing
var arr = ['javascript', 'typescript', 'es6'];
var searchValue = (value) => {
return arr.filter(item => {
return item. indexOf(value) > -1;
});
}
console.log(searchValue ('script'));
var a = [1, 2, 3, 4];
function sumUsingFunction (acc, value) {
return acc + value;
}
var sumOfArrayUsingFunc = a.reduce(sumUsingFunc);
for (var i=1; i <= 15; i++){
if (i % 15 == 0) console.log("FizzBuzz");
else if (i % 3 == 0) console.log("Fizz");
else if (i % 5 == 0) console.log("Buzz");
else console.log(i);
}
Output:
1
2
Fizz
4
Buzz
Fizz
7
8
Fizz
Buzz
11
Fizz
13
14
FizzBuzz
Solution - 02
for (var i = 1; i <= 15; i++) {
var f = i % 3 == 0, b = i % 5 == 0;
console.log(f ? b ? "FizzBuzz" : "Fizz" : b ? "Buzz" : i);
}
var output = (function(x) {
delete x;
return x;
})(0);
console.log(output);
The code above will output 0 as output. delete operator is used to delete a property from an object. Here x is not an object it’s local variable. delete operator doesn’t affect local variables.
var x = 1;
var output = (function() {
delete x;
return x;
})();
console.log(output);
The code above will output 1 as output. delete operator is used to delete a property from an object. Here x is not an object it’s global variable of type number.
var x = { foo : 1};
var output = (function() {
delete x.foo;
return x.foo;
})();
console.log(output);
The code above will output undefined as output. delete operator is used to delete a property from an object. Here x is an object which has foo as a property and from a self-invoking function, we are deleting the foo property of object x and after deletion, we are trying to reference deleted property foo which result undefined.
var Employee = {
company: 'xyz'
}
var emp1 = Object.create(Employee);
delete emp1.company
console.log(emp1.company);
The code above will output xyz as output. Here emp1 object got company as prototype property. delete operator doesn’t delete prototype property.
emp1 object doesn’t have company as its own property. you can test it console.log(emp1.hasOwnProperty('company')); //output : false However, we can delete company property directly from Employee object using delete Employee.company or we can also delete from emp1 object using __proto__ property delete emp1.__proto__.company.
var trees = ["xyz", "xxxx", "test", "ryan", "apple"];
delete trees[3];
console.log(trees.length);
The code above will output 5 as output. When we used delete operator for deleting an array element then, the array length is not affected by this. This holds even if you deleted all elements of an array using delete operator.
So when delete operator removes an array element that deleted element is no longer present in the array. In place of value at deleted index undefined x 1 in chrome and undefined is placed at the index. If you do console.log(trees) output ["xyz", "xxxx", "test", undefined × 1, "apple"] in Chrome and in Firefox ["xyz", "xxxx", "test", undefined, "apple"].
var bar = true;
console.log(bar + 0);
console.log(bar + "xyz");
console.log(bar + true);
console.log(bar + false);
The code above will output 1, "truexyz", 2, 1 as output. Here’s a general guideline for the plus operator:
var z = 1, y = z = typeof y;
console.log(y);
The code above will print string "undefined" as output. According to associativity rule operator with the same precedence are processed based on their associativity property of operator. Here associativity of the assignment operator is Right to Left so first typeof y will evaluate first which is string "undefined" and assigned to z and then y would be assigned the value of z. The overall sequence will look like that:
var z;
z = 1;
var y;
z = typeof y;
y = z;
// NFE (Named Function Expression)
var foo = function bar() { return 12; };
typeof bar();
The output will be Reference Error. To fix the bug we can try to rewrite the code a little bit:
Sample 1
var bar = function() { return 12; };
typeof bar();
or
Sample 2
function bar() { return 12; };
typeof bar();
The function definition can have only one reference variable as a function name, In sample 1 bar is reference variable which is pointing to anonymous function and in sample 2 we have function statement and bar is the function name.
var foo = function bar() {
// foo is visible here
// bar is visible here
console.log(typeof bar()); // Works here :)
};
// foo is visible here
// bar is undefined here
bar();
(function abc(){console.log('something')})();
function bar(){console.log('bar got called')};
The output will be :
bar got called
something
Since the function is called first and defined during parse time the JS engine will try to find any possible parse time definitions and start the execution loop which will mean function is called first even if the definition is post another function.
var salary = "1000$";
(function () {
console.log("Original salary was " + salary);
var salary = "5000$";
console.log("My New Salary " + salary);
})();
The code above will output: undefined, 5000$ because of hoisting. In the code presented above, you might be expecting salary to retain it values from outer scope until the point that salary was re-declared in the inner scope. But due to hoisting salary value was undefined instead. To understand it better have a look of the following code, here salary variable is hoisted and declared at the top in function scope. When we print its value using console.log the result is undefined. Afterwards the variable is redeclared and the new value "5000$" is assigned to it.
var salary = "1000$";
(function () {
var salary = undefined;
console.log("Original salary was " + salary);
salary = "5000$";
console.log("My New Salary " + salary);
})();
function User(name) {
this.name = name || "JsGeeks";
}
var person = new User("xyz")["location"] = "USA";
console.log(person);
The output of above code would be "USA". Here new User("xyz") creates a brand new object and created property location on that and USA has been assigned to object property location and that has been referenced by the person.
Let say new User("xyz") created a object called foo. The value "USA" will be assigned to foo["location"], but according to ECMAScript Specification , pt 12.14.4 the assignment will itself return the rightmost value: in our case it’s "USA".
Then it will be assigned to person.
To better understand what’s going on here, try to execute this code in console, line by line:
function User(name) {
this.name = name || "JsGeeks";
}
var person;
var foo = new User("xyz");
foo["location"] = "USA";
// the console will show you that the result of this is "USA"
var strA = "hi there";
var strB = strA;
strB="bye there!";
console.log (strA)
The output will 'hi there' because we’re dealing with strings here. Strings are
passed by value, that is, copied.
var objA = {prop1: 42};
var objB = objA;
objB.prop1 = 90;
console.log(objA)
The output will {prop1: 90} because we’re dealing with objects here. Objects are
passed by reference, that is, objA and objB point to the same object in memory.
var objA = {prop1: 42};
var objB = objA;
objB = {};
console.log(objA)
The output will {prop1: 42}.
When we assign objA to objB, the objB variable will point
to the same object as the objB variable.
However, when we reassign objB to an empty object, we simply change where objB variable references to.
This doesn’t affect where objA variable references to.
var arrA = [0,1,2,3,4,5];
var arrB = arrA;
arrB[0]=42;
console.log(arrA)
The output will be [42,1,2,3,4,5].
Arrays are object in JavaScript and they are passed and assigned by reference. This is why
both arrA and arrB point to the same array [0,1,2,3,4,5]. That’s why changing the first
element of the arrB will also modify arrA: it’s the same array in the memory.
var arrA = [0,1,2,3,4,5];
var arrB = arrA.slice();
arrB[0]=42;
console.log(arrA)
The output will be [0,1,2,3,4,5].
The slice function copies all the elements of the array returning the new array. That’s why
arrA and arrB reference two completely different arrays.
var arrA = [{prop1: "value of array A!!"}, {someProp: "also value of array A!"}, 3,4,5];
var arrB = arrA;
arrB[0].prop1=42;
console.log(arrA);
The output will be [{prop1: 42}, {someProp: "also value of array A!"}, 3,4,5].
Arrays are object in JS, so both varaibles arrA and arrB point to the same array. Changing
arrB[0] is the same as changing arrA[0]
var arrA = [{prop1: "value of array A!!"}, {someProp: "also value of array A!"},3,4,5];
var arrB = arrA.slice();
arrB[0].prop1=42;
arrB[3] = 20;
console.log(arrA);
The output will be [{prop1: 42}, {someProp: "also value of array A!"}, 3,4,5].
The slice function copies all the elements of the array returning the new array. However,
it doesn’t do deep copying. Instead it does shallow copying. You can imagine slice implemented like this:
function slice(arr) {
var result = [];
for (i = 0; i< arr.length; i++) {
result.push(arr[i]);
}
return result;
}
Look at the line with result.push(arr[i]). If arr[i] happens to be a number or string,
it will be passed by value, in other words, copied. If arr[i] is an object, it will be passed by reference.
In case of our array arr[0] is an object {prop1: "value of array A!!"}. Only the reference
to this object will be copied. This effectively means that arrays arrA and arrB share first
two elements.
This is why changing the property of arrB[0] in arrB will also change the arrA[0].
Answer: 4) ReferenceError: employeeId is not defined
console.log(employeeId);
var employeeId = '19000';
Answer: 2) undefined
var employeeId = '1234abe';
(function(){
console.log(employeeId);
var employeeId = '122345';
})();
Answer: 2) undefined
var employeeId = '1234abe';
(function() {
console.log(employeeId);
var employeeId = '122345';
(function() {
var employeeId = 'abc1234';
}());
}());
Answer: 2) undefined
(function() {
console.log(typeof displayFunc);
var displayFunc = function(){
console.log("Hi I am inside displayFunc");
}
}());
Answer: 1) undefined
var employeeId = 'abc123';
function foo(){
employeeId = '123bcd';
return;
}
foo();
console.log(employeeId);
Answer: 2) ‘123bcd’
var employeeId = 'abc123';
function foo() {
employeeId = '123bcd';
return;
function employeeId() {}
}
foo();
console.log(employeeId);
Answer: 3) ‘abc123’
var employeeId = 'abc123';
function foo() {
employeeId();
return;
function employeeId() {
console.log(typeof employeeId);
}
}
foo();
Answer: 2) ‘function’
function foo() {
employeeId();
var product = 'Car';
return;
function employeeId() {
console.log(product);
}
}
foo();
Answer: 1) undefined
(function foo() {
bar();
function bar() {
abc();
console.log(typeof abc);
}
function abc() {
console.log(typeof bar);
}
}());
Answer: 3) function function
(function() {
'use strict';
var person = {
name: 'John'
};
person.salary = '10000$';
person['country'] = 'USA';
Object.defineProperty(person, 'phoneNo', {
value: '8888888888',
enumerable: true
})
console.log(Object.keys(person));
})();
Answer: 3) [“name”, “salary”, “country”, “phoneNo”]
(function() {
'use strict';
var person = {
name: 'John'
};
person.salary = '10000$';
person['country'] = 'USA';
Object.defineProperty(person, 'phoneNo', {
value: '8888888888',
enumerable: false
})
console.log(Object.keys(person));
})();
Answer: 4) [“name”, “salary”, “country”]
(function() {
var objA = {
foo: 'foo',
bar: 'bar'
};
var objB = {
foo: 'foo',
bar: 'bar'
};
console.log(objA == objB);
console.log(objA === objB);
}());
Answer: 2) false false
(function() {
var objA = new Object({foo: "foo"});
var objB = new Object({foo: "foo"});
console.log(objA == objB);
console.log(objA === objB);
}());
Answer: 2) false false
(function() {
var objA = Object.create({
foo: 'foo'
});
var objB = Object.create({
foo: 'foo'
});
console.log(objA == objB);
console.log(objA === objB);
}());
Answer: 2) false false
(function() {
var objA = Object.create({
foo: 'foo'
});
var objB = Object.create(objA);
console.log(objA == objB);
console.log(objA === objB);
}());
Answer: 2) false false
(function() {
var objA = Object.create({
foo: 'foo'
});
var objB = Object.create(objA);
console.log(objA.toString() == objB.toString());
console.log(objA.toString() === objB.toString());
}());
Answer: 4) true true
(function() {
var objA = Object.create({
foo: 'foo'
});
var objB = objA;
console.log(objA == objB);
console.log(objA === objB);
console.log(objA.toString() == objB.toString());
console.log(objA.toString() === objB.toString());
}());
Answer: 3) true true true true
(function() {
var objA = Object.create({
foo: 'foo'
});
var objB = objA;
objB.foo = 'bar';
console.log(objA.foo);
console.log(objB.foo);
}());
Answer: 2) bar bar
(function() {
var objA = Object.create({
foo: 'foo'
});
var objB = objA;
objB.foo = 'bar';
delete objA.foo;
console.log(objA.foo);
console.log(objB.foo);
}());
Answer: 3) foo foo
(function() {
var objA = {
foo: 'foo'
};
var objB = objA;
objB.foo = 'bar';
delete objA.foo;
console.log(objA.foo);
console.log(objB.foo);
}());
Answer: 2) undefined undefined
(function() {
var array = new Array('100');
console.log(array);
console.log(array.length);
}());
Answer: 3) [“100”] 1
(function() {
var array1 = [];
var array2 = new Array(100);
var array3 = new Array(['1',2,'3',4,5.6]);
console.log(array1);
console.log(array2);
console.log(array3);
console.log(array3.length);
}());
Answer: 1) [] [] [Array[5]] 1
(function () {
var array = new Array('a', 'b', 'c', 'd', 'e');
array[10] = 'f';
delete array[10];
console.log(array.length);
}());
Answer: 1) 11
(function(){
var animal = ['cow','horse'];
animal.push('cat');
animal.push('dog','rat','goat');
console.log(animal.length);
})();
Answer: 3) 6
(function(){
var animal = ['cow','horse'];
animal.push('cat');
animal.unshift('dog','rat','goat');
console.log(animal);
})();
Answer: 1) [ ‘dog’, ‘rat’, ‘goat’, ‘cow’, ‘horse’, ‘cat’ ]
(function(){
var array = [1,2,3,4,5];
console.log(array.indexOf(2));
console.log([{name: 'John'},{name : 'John'}].indexOf({name:'John'}));
console.log([[1],[2],[3],[4]].indexOf([3]));
console.log("abcdefgh".indexOf('e'));
})();
Answer: 1) 1 -1 -1 4
(function(){
var array = [1,2,3,4,5,1,2,3,4,5,6];
console.log(array.indexOf(2));
console.log(array.indexOf(2,3));
console.log(array.indexOf(2,10));
})();
Answer: 2) 1 6 -1
(function(){
var numbers = [2,3,4,8,9,11,13,12,16];
var even = numbers.filter(function(element, index){
return element % 2 === 0;
});
console.log(even);
var containsDivisibleby3 = numbers.some(function(element, index){
return element % 3 === 0;
});
console.log(containsDivisibleby3);
})();
Answer: 3) [ 2, 4, 8, 12, 16 ] true
(function(){
var containers = [2,0,false,"", '12', true];
var containers = containers.filter(Boolean);
console.log(containers);
var containers = containers.filter(Number);
console.log(containers);
var containers = containers.filter(String);
console.log(containers);
var containers = containers.filter(Object);
console.log(containers);
})();
Answer: 1) [ 2, ‘12’, true ] [ 2, ‘12’, true ] [ 2, ‘12’, true ] [ 2, ‘12’, true ]
(function(){
var list = ['foo','bar','john','ritz'];
console.log(list.slice(1));
console.log(list.slice(1,3));
console.log(list.slice());
console.log(list.slice(2,2));
console.log(list);
})();
Answer: 1) [ ‘bar’, ‘john’, ‘ritz’ ] [ ‘bar’, ‘john’ ] [ ‘foo’, ‘bar’, ‘john’, ‘ritz’ ] [] [ ‘foo’, ‘bar’, ‘john’, ‘ritz’ ]
(function(){
var list = ['foo','bar','john'];
console.log(list.splice(1));
console.log(list.splice(1,2));
console.log(list);
})();
Answer: 1. [ ‘bar’, ‘john’ ] [] [ ‘foo’ ]
(function(){
var arrayNumb = [2, 8, 15, 16, 23, 42];
arrayNumb.sort();
console.log(arrayNumb);
})();
Answer: 3. [ 15, 16, 2, 23, 42, 8 ]
function funcA(){
console.log("funcA ", this);
(function innerFuncA1(){
console.log("innerFunc1", this);
(function innerFunA11(){
console.log("innerFunA11", this);
})();
})();
}
console.log(funcA());
Answer: 1)
var obj = {
message: "Hello",
innerMessage: !(function() {
console.log(this.message);
})()
};
console.log(obj.innerMessage);
Answer: 4) undefined true
var obj = {
message: "Hello",
innerMessage: function() {
return this.message;
}
};
console.log(obj.innerMessage());
Answer: 1) Hello
var obj = {
message: 'Hello',
innerMessage: function () {
(function () {
console.log(this.message);
}());
}
};
console.log(obj.innerMessage());
Answer: 3) undefined
var obj = {
message: 'Hello',
innerMessage: function () {
var self = this;
(function () {
console.log(self.message);
}());
}
};
console.log(obj.innerMessage());
Answer: 2) ‘Hello’
function myFunc(){
console.log(this.message);
}
myFunc.message = "Hi John";
console.log(myFunc());
Answer: 3) undefined
function myFunc(){
console.log(myFunc.message);
}
myFunc.message = "Hi John";
console.log(myFunc());
Answer: 2) ‘Hi John’
function myFunc() {
myFunc.message = 'Hi John';
console.log(myFunc.message);
}
console.log(myFunc());
Answer: 2) ‘Hi John’
function myFunc(param1,param2) {
console.log(myFunc.length);
}
console.log(myFunc());
console.log(myFunc("a","b"));
console.log(myFunc("a","b","c","d"));
Answer: a) 2 2 2
function myFunc() {
console.log(arguments.length);
}
console.log(myFunc());
console.log(myFunc("a","b"));
console.log(myFunc("a","b","c","d"));
Answer: 2) 0 2 4
function Person(name, age){
this.name = name || "John";
this.age = age || 24;
this.displayName = function(){
console.log(this.name);
}
}
Person.name = "John";
Person.displayName = function(){
console.log(this.name);
}
var person1 = new Person('John');
person1.displayName();
Person.displayName();
Answer: 1) John Person
function passWordMngr() {
var password = '12345678';
this.userName = 'John';
return {
pwd: password
};
}
// Block End
var userInfo = passWordMngr();
console.log(userInfo.pwd);
console.log(userInfo.userName);
Answer: 3) 12345678 undefined
var employeeId = 'aq123';
function Employee() {
this.employeeId = 'bq1uy';
}
console.log(Employee.employeeId);
Answer: 4) undefined
var employeeId = 'aq123';
function Employee() {
this.employeeId = 'bq1uy';
}
console.log(new Employee().employeeId);
Employee.prototype.employeeId = 'kj182';
Employee.prototype.JobId = '1BJKSJ';
console.log(new Employee().JobId);
console.log(new Employee().employeeId);
Answer: 2) bq1uy 1BJKSJ bq1uy
var employeeId = 'aq123';
(function Employee() {
try {
throw 'foo123';
} catch (employeeId) {
console.log(employeeId);
}
console.log(employeeId);
}());
Answer: 1) foo123 aq123
(function() {
var greet = 'Hello World';
var toGreet = [].filter.call(greet, function(element, index) {
return index > 5;
});
console.log(toGreet);
}());
Answer: 4) [ ‘W’, ‘o’, ‘r’, ‘l’, ‘d’ ]
(function() {
var fooAccount = {
name: 'John',
amount: 4000,
deductAmount: function(amount) {
this.amount -= amount;
return 'Total amount left in account: ' + this.amount;
}
};
var barAccount = {
name: 'John',
amount: 6000
};
var withdrawAmountBy = function(totalAmount) {
return fooAccount.deductAmount.bind(barAccount, totalAmount);
};
console.log(withdrawAmountBy(400)());
console.log(withdrawAmountBy(300)());
}());
Answer: 1) Total amount left in account: 5600 Total amount left in account: 5300
(function() {
var fooAccount = {
name: 'John',
amount: 4000,
deductAmount: function(amount) {
this.amount -= amount;
return this.amount;
}
};
var barAccount = {
name: 'John',
amount: 6000
};
var withdrawAmountBy = function(totalAmount) {
return fooAccount.deductAmount.apply(barAccount, [totalAmount]);
};
console.log(withdrawAmountBy(400));
console.log(withdrawAmountBy(300));
console.log(withdrawAmountBy(200));
}());
Answer: 1) 5600 5300 5100
(function() {
var fooAccount = {
name: 'John',
amount: 6000,
deductAmount: function(amount) {
this.amount -= amount;
return this.amount;
}
};
var barAccount = {
name: 'John',
amount: 4000
};
var withdrawAmountBy = function(totalAmount) {
return fooAccount.deductAmount.call(barAccount, totalAmount);
};
console.log(withdrawAmountBy(400));
console.log(withdrawAmountBy(300));
console.log(withdrawAmountBy(200));
}());
Answer: 2) 3600 3300 3100
(function greetNewCustomer() {
console.log('Hello ' + this.name);
}.bind({
name: 'John'
})());
Answer: 1) Hello John
function getDataFromServer(apiUrl){
var name = "John";
return {
then : function(fn){
fn(name);
}
}
}
getDataFromServer('www.google.com').then(function(name){
console.log(name);
});
Answer: 1) John
(function(){
var arrayNumb = [2, 8, 15, 16, 23, 42];
Array.prototype.sort = function(a,b){
return a - b;
};
arrayNumb.sort();
console.log(arrayNumb);
})();
(function(){
var numberArray = [2, 8, 15, 16, 23, 42];
numberArray.sort(function(a,b){
if(a == b){
return 0;
}else{
return a < b ? -1 : 1;
}
});
console.log(numberArray);
})();
(function(){
var numberArray = [2, 8, 15, 16, 23, 42];
numberArray.sort(function(a,b){
return a-b;
});
console.log(numberArray);
})();
Answer: 1) [ 2, 8, 15, 16, 23, 42 ] [ 2, 8, 15, 16, 23, 42 ] [ 2, 8, 15, 16, 23, 42 ]
(function(){
function sayHello(){
var name = "Hi John";
return
{
fullName: name
}
}
console.log(sayHello().fullName);
})();
Answer: 4) Uncaught TypeError: Cannot read property ‘fullName’ of undefined
function getNumber(){
return (2,4,5);
}
var numb = getNumber();
console.log(numb);
Answer: 1) 5
function getNumber(){
return;
}
var numb = getNumber();
console.log(numb);
Answer: 2) undefined
function mul(x){
return function(y){
return [x*y, function(z){
return x*y + z;
}];
}
}
console.log(mul(2)(3)[0]);
console.log(mul(2)(3)[1](4));
Answer: 1) 6, 10
function mul(x) {
return function(y) {
return {
result: x * y,
sum: function(z) {
return x * y + z;
}
};
};
}
console.log(mul(2)(3).result);
console.log(mul(2)(3).sum(4));
Answer: 1) 6, 10
function mul(x) {
return function(y) {
return function(z) {
return function(w) {
return function(p) {
return x * y * z * w * p;
};
};
};
};
}
console.log(mul(2)(3)(4)(5)(6));
Answer: 1) 720
foo?var foo = 10 + '20';
Answer: '1020', because of type coercion from Number to String
add(2, 5); // 7
add(2)(5); // 7
Answer: A general solution for any number of parameters
'use strict';
let sum = (arr) => arr.reduce((a, b) => a + b);
let addGenerator = (numArgs, prevArgs) => {
return function () {
let totalArgs = prevArgs.concat(Array.from(arguments));
if (totalArgs.length === numArgs) {
return sum(totalArgs);
}
return addGenerator(numArgs, totalArgs);
};
};
let add = addGenerator(2, []);
add(2, 5); // 7
add(2)(5); // 7
add()(2, 5); // 7
add()(2)(5); // 7
add()()(2)(5); // 7
"i'm a lasagna hog".split("").reverse().join("");
Answer: It’s actually a reverse method for a string - 'goh angasal a m\'i'
window.foo?( window.foo || ( window.foo = "bar" ) );
Answer: Always 'bar'
var foo = "Hello";
(function() {
var bar = " World";
alert(foo + bar);
})();
alert(foo + bar);
Answer:
Hello WorldReferenceError: bar is not definedfoo.length?var foo = [];
foo.push(1);
foo.push(2);
Answer: .push is mutable - 2
foo.x?var foo = {n: 1};
var bar = foo;
foo.x = foo = {n: 2};
Answer: undefined. Rather, bar.x is {n: 2}.
foo.x = foo = {n: 2} is the same as foo.x = (foo = {n: 2}). It is because
a left term is first referenced and then a right term is evaluated when an
assignment is performed in JavaScript. When foo.x is referenced, it refers
to an original object, {n: 1}. So, when the result of the right term, {n:
2}, is evaluated, it will assigned to the original object, which is at the
moment referenced by bar.
console.log('one');
setTimeout(function() {
console.log('two');
}, 0);
console.log('three');
Answer: one, three and two. It’s because console.log('two'); will be
invoked in the next event loop.
The output is going to be 33. Since 1 and 2 are numeric values, the result of first two digits is going to be a numeric value 3. The next digit is a string type value because of that the addition of numeric value 3 and string type value 3 is just going to be a concatenation value 33.
function countCharacters(str) {
return str.replace(/ /g, '').toLowerCase().split('').reduce((arr, character) => {
if (character in arr) {
arr[character]++;
} else {
arr[character] = 1;
}
return arr;
}, {});
}
console.log(countCharacters("the brown fox jumps over the lazy dog"));
foo?var foo = 10 + '20';
Answer: '1020', because of type coercion from Number to String
add(2, 5); // 7
add(2)(5); // 7
Answer: A general solution for any number of parameters
'use strict';
let sum = (arr) => arr.reduce((a, b) => a + b);
let addGenerator = (numArgs, prevArgs) => {
return function () {
let totalArgs = prevArgs.concat(Array.from(arguments));
if (totalArgs.length === numArgs) {
return sum(totalArgs);
}
return addGenerator(numArgs, totalArgs);
};
};
let add = addGenerator(2, []);
add(2, 5); // 7
add(2)(5); // 7
add()(2, 5); // 7
add()(2)(5); // 7
add()()(2)(5); // 7
"i'm a lasagna hog".split("").reverse().join("");
Answer: It’s actually a reverse method for a string - 'goh angasal a m\'i'
window.foo?( window.foo || ( window.foo = "bar" ) );
Answer: Always 'bar'
var foo = "Hello";
(function() {
var bar = " World";
alert(foo + bar);
})();
alert(foo + bar);
Answer:
Hello WorldReferenceError: bar is not definedfoo.length?var foo = [];
foo.push(1);
foo.push(2);
Answer: .push is mutable - 2
foo.x?var foo = {n: 1};
var bar = foo;
foo.x = foo = {n: 2};
Answer: undefined. Rather, bar.x is {n: 2}.
foo.x = foo = {n: 2} is the same as foo.x = (foo = {n: 2}). It is because
a left term is first referenced and then a right term is evaluated when an
assignment is performed in JavaScript. When foo.x is referenced, it refers
to an original object, {n: 1}. So, when the result of the right term, {n:
2}, is evaluated, it will assigned to the original object, which is at the
moment referenced by bar.
console.log('one');
setTimeout(function() {
console.log('two');
}, 0);
console.log('three');
Answer: one, three and two. It’s because console.log('two'); will be
invoked in the next event loop.
// if( x <= 100 ) {...}
if( !(x > 100) ) {...}
Answer: NaN <= 100 is false and NaN > 100 is also false, so if the value of x is NaN, the statements are not the same.
The same holds true for any value of x that being converted to Number, returns NaN, e.g.: undefined, [1,2,5], {a:22}, etc.
f = g = 0;
(function () {
try {
f = function() {
return f();
};
f();
} catch (e) {
return g++ && f();
} finally {
return ++g;
}
function f() { g += 5; return 0; }
}) ();
f = g = 0;
(function () {
try {
f = function() {
return f();
} && f();
} catch (e) {
return g++ && f();
} finally {
return ++g;
}
function f() { g += 5; return 0; }
}) ();
function b(b) {
return this.b && b(b)
}
b(b.bind(b))
c = (c) => {
return this.c && c(c)
}
c(c.bind(c))
var g = 0;
g = 1 && g++;
console.log(g);
!function(){}()
function(){}()
true && function(){}()
(function(){})()
function(){}
!function(){}
var a = b = true, c = (a) => a;
(function a(a = c(b).a = c = () => a) { return a(); })()
var a = true;
(a = function () { return a })()
var v = 0;
try {
throw v = (function(c) { throw v = function(a){ return v; } })();
} catch (e) {
console.log (e()());
}
const arr = [10, 12, 15, 21];
for (var i = 0; i < arr.length; i++) {
setTimeout(function() {
console.log('Index: ' + i + ', element: ' + arr[i]);
}, 3000);
}
var output = (function(x) {
delete x;
return x;
})(0);
console.log(output);
var Employee = {
company: 'xyz'
}
var emp1 = Object.create(Employee);
delete emp1.company
console.log(emp1.company);
duplicate([1, 2, 3, 4, 5]); // [1,2,3,4,5,1,2,3,4,5]
function duplicate(arr) {
return arr.concat(arr);
}
duplicate([1, 2, 3, 4, 5]); // [1,2,3,4,5,1,2,3,4,5]
var arr = [10, 32, 65, 2];
for (var i = 0; i < arr.length; i++) {
setTimeout(function() {
console.log('The index of this number is: ' + i);
}, 3000);
}
For ES6, you can just replace var i with let i.
For ES5, you need to create a function scope like here:
var arr = [10, 32, 65, 2];
for (var i = 0; i < arr.length; i++) {
setTimeout(function(j) {
return function () {
console.log('The index of this number is: ' + j)
};
}(i), 3000);
}
console.log(eval("10 + 10")); // 20
console.log(eval("5 + 5" + 10)); // 515
console.log(eval("5 + 5 + 5" + 10)); // 520
console.log(eval(10 + "5 + 5")); // 110
console.log(eval(10 + "5 + 5 + 5")); // 115
var x = 10;
var y = 20;
var a = eval("x * y") + "<br>";
var b = eval("2 + 2") + "<br>";
var c = eval("x + 30") + "<br>";
let result = a + b + c;
console.log(result); // 200<br>4<br>40<br>
// Example 01:
var prices = [12, 20, 18];
var newPriceArray = [...prices];
console.log(newPriceArray);
// Example 02:
var alphabets = ["A", ..."BCD", "E"];
console.log(alphabets);
// Example 03:
var prices = [12, 20, 18];
var maxPrice = Math.max(...prices);
console.log(maxPrice);
// Example 04:
var max = Math.max(..."43210");
console.log(max);
// Example 05:
const fruits = ["apple", "orange"];
const vegetables = ["carrot", "potato"];
const result = ['bread', ...vegetables, 'chicken', ...fruits];
console.log(result);
// Example 06:
const country = "USA";
console.log([...country]);