10 Commonly asked Javascript Interview Questions 2018

#javascriptquestions

Javascript is one of most popular programming language for the web. It is widely used for creating interactive client-side web applications and games. Javascript can be also used as server-side programming language. It is dynamic, weakly typed, prototype-based and multi-paradigm high-level programming language.

Here we have listed 10 Common Javascript Interview Questions with their answers

1. What will be the output of variable x,y,z?

var x=10;
var y=x++;
var z=++x;
console.log(x,y,z)
Ans: It will log 12,10,12

2. What will be output of 0==-0

Answer: output of 0==-0 is true

3. What is the output of below code

function xyz () {
var abc = "hello Js";
function abc () {
return 54;
}
return abc;
}
console.log(xyz())
Answer: The above code will output hello Js.

4. How to create an object in JavaScript?

Ans: Creating an object In Javascript var object ={ name: "obj", age: 10 };

5. Explain prototypal Inheritance in JavaScript?

In JS every object has a property called a prototype, where we can add methods to it and when you create another object from these the newly created object will automatically inherit its parent’s property.

6. Explain callback in JavaScript?

A callback is a plain JavaScript function passed to some method as an argument or option. Some callbacks are just events, called to give the user a chance to react when a certain state is triggered.

7. How would you empty the below array in JavaScript?

Var emptyArray = ['this', 'array', 'is', 'full'];
Ans: Use below line of code to empty an array in JavaScript

emptyArray.length = 0;

emptyArray.splice(0, emptyArray.length);

while(emptyArray.length){
emptyArray.pop();
}

emptyArray = []

8. What will be output of below code?

var lorem = { ipsum : 1};
var output = (function(){
delete lorem.ipsum;
return lorem.ipsum;
})();

console.log(output);
Ans: The output would be undefined because the delete operator removed the property "ipsum" from the object "lorem" before the object was returned. When you reference a deleted property, the result is undefined.