Basics

Question 1

What is coercision

Answer 1

Process of converting a variable to string for representational purpose

Question 2

“99.99” == 99.99

Answer 2

True, the RHS is converted to string

Question 3

What typing is used in JS

Answer 3

Dynamic typing

Question 4

How to take only two values from a number

Answer 4

number.toFixed(2)

Question 5

function outer() {
	var a = 1;

	function inner() {
		var b = 2;
        	console.log( a + b );
	}

inner();

console.log( a ); }

outer();
Output of this problem

Answer 5

3

1

Question 6

a = null;
typeof a;

what is the output

Answer 6

object

Question 7

Declare array

Answer 7

var arr = [1,2,3];

Question 8

what non boolean values when coerced to bool will give false value

Answer 8

0
-0
""
nan
null
undefined
false

Question 9

== checks for

Answer 9

Value equality, while allowing for coercion

Question 10

=== checks

Answer 10

Value and type equality

Question 11

obj a = { a:10}
obj b = {a:9}

a ==b
a===b

Answer 11

The checks are done only for reference equals and checking the underlying values

Question 12

var a = [1,2,3];
var b = [1,2,3];
var c = "1,2,3";

a == c;
b == c;
a == b;

Answer 12

true
true
false

Arrays are coerced into string by default separated by commas

Question 13

Scope of b and c and why?

function foo() {
	var a = 1;

	if (a >= 1) {
		let b = 2;

		while (b < 5) {
			let c = b * 2;
			b++;

		console.log( a + c );
	}
} }

foo();

Answer 13

b will belong only to the if statement and thus not to the whole foo() function’s scope. Similarly, c belongs only to the while loop

Question 14

Immediately Invoked Function Expressions (IIFEs) example

Answer 14

(function(){
return 10;
})();

Question 15

Closure

Answer 15

Having one function inside other and the concept is the child function remebers the variable in scope for the parent function even after the parenr function has returned

Question 16

What is the output

function foo() {
	console.log( this.bar );
}

var bar = “global”;

var obj1 = {
	bar: "obj1",
	foo: foo
};

var obj2 = {
	bar: "obj2"
};

// ——–

foo();
obj1.foo();
foo.call( obj2 );
new foo();

Answer 16

“global”
“obj1”
“obj2”
“Undefined” //because new creates a brand new this object

Question 17

What does Object.Create() do ?

Answer 17

The Object.create() method creates a new object, using an existing object as the prototype of the newly created object

Question 18

What is teh output ?
x = 10
console.log(x !== x)
x = NaN
console.log(x !== x)

Answer 18

True
False

NaN the only value in the whole language that is not equal to itself.

Question 19

What is Polyfilling?

Answer 19

Providing stubs for methods which are not present in the current version of JS

Question 20

What is Transpiling?

Answer 20

Converting Newer JS syntax into a form the browser understands

Question 21

How to get all objects passed to a function call ?

Answer 21

Every function has the “arguments” object, which can be indexed to get the values passed to it

Question 22

Names of some Transpilers?

Answer 22

Babel and Traceur

Question 23

document object,
console.log()
alert()what are they?

Answer 23

They are not provided by the JS engine, nor is it particularly controlled by the JavaScript specification.
They may be implemented in other languages and given to us by the browsers to use from JS code

Question 24

how does anonymous function call itself to perform recursion

Answer 24

It can use “arguments.callee”, but it is deprcated