JavaScript Interview Questions
This page consists of JavaScript interview questions and answers.
undefined
not defined
When we declare a variable but do not assign any value to it then by default it is assigned the undefined value.
The following code will print undefined.
var x; console.log(x);
If we try to access a variable that is not declared then we get the not defined error and the script stops to execute further.
The following code will give us not defined error.
console.log(y);
Output:
Uncaught ReferenceError: y is not defined
Following are the primitive data types in JavaScript.
Following are the non-primitive data types in JavaScript.
for (var i = 0; i < 3; i++) { var str = ""; for (var j = 0; j <= i; j++) { str += j + " "; } console.log(str); }
The output for the above code is the following.
0 0 1 0 1 2
var user = { name: 'Yusuf Shakeel', score: 10, username: 'yusufshakeel' }; var score = user.score; score += 10; user['score'] = score; console.log(user);
The above code will give us the following result.
{ name: 'Yusuf Shakeel', score: 20, username: 'yusufshakeel' }
function foo(x) { var y = x + 10; function bar(y) { console.log(x); console.log(y); } bar(y); } foo(10);
The output for the above code is.
10 20
function bar(x) { return function foo() { console.log(x); } } var x = bar(10); x();
The answer for the above code is 10.
The default return value is undefined for a function if no return statement is present.
var str = "Hello".split('').reverse().join(''); console.log(str);
The output of the above code is "olleH".
var movie = (function() { return { name: 'Avengers: Infinity War', getName: function() { return this.name; } }; }()); console.log(movie.getName());
The above code will print "Avengers: Infinity War".