Difference between != and !== [duplicate]

Question

In this function, when it is compared the lenght of the array it is used != operator and when it is comparing all elements of the array it is using !== operator. Why?! Thx.

var a = [1,2,3];
var b = [2,3,4];

function equalArrays(a,b){      
    if(a.length != b.length) return false;
    for(var i = 0; i < a.length; i++)
        if(a[i] ==! b[i]) return false;
    return true;

}

Answer 1

= is an assignment operator, e.g. If you run var x = 1; then x will have the value of 1.

== (or !=) is a comparison operator that checks if the value of something is equal to the value of something else. e.g. if(x == 1) will evaluate to true and so will if(x == true) because 1 will evaluate to true and 0 evaluate to false.

=== (or !==) is another comparison operator that checks if the value of something is equal to the value of, and is the same type as something else. e.g. if(x === 1) will evaluate to true however, if(x === true) will evaluate to false because 1 (the value of x) is an integer and true is a boolean.

Answer 2

The triple equals (===) not only checks the value, but the type.

The following are true:

false == false
false == null
false == undefined
false == 0
2 == "2"

The following are NOT true:

false === null
false === undefined
false === 0
2 === "2"