Why javascript treats 0 equal to empty string? [duplicate]

Answer 1

== operator in javascript don't compare types so 0=='' === true (because as a number string '' evaluates to 0) or 0==false === true (because bool false evaluates to 0) to compare types to you can use === operator.

Here you'll find useful information about comparison.

Answer 2

0, "" (Empty String), false all technically have the same value, when typecasted. If you need to strictly treat them, you can use ===.

It is the same with similar programming languages, like PHP.

var a = 0;
var b = ''; //empty string
if(a == b){
    console.log('equal'); //this is printed in console
}else{
    console.log('not equal');
}

To make a strict comparison:

if(a === b){
    console.log('equal');
}else{
    console.log('not equal'); //this is printed in console
}

Answer 3

Because of coercion. It is usually a better idea to use === for comparisons in JavaScript.

Answer 4

In most programming language(including javascript) ""(string), 0(integer), \x0(null) losely mean the same thing: "empty". What's happening is your javascript engine finds "" == 0 false, due to the == it converts 0 to an integer. Again this is false, so it converts 0 to null which is false, so then it converts 0 to an empty string. (Not sure if this is the correct order of conversion). To make the condition "exact" match(no conversion) use === inplace of ==

Answer 5

Because empty string represented as number is zero. If you compare apples and oranges you should think of how your particular orange would look if it were an apple.

Answer 6

Quoting the doc (MDN):

Equal (==)

If the two operands are not of the same type, JavaScript converts the operands then applies strict comparison. If either operand is a number or a boolean, the operands are converted to numbers if possible; else if either operand is a string, the other operand is converted to a string if possible.

As a operand type here is Number, b gets converted to Number as well. And Number('') evaluates to 0.

This can be quite surprising sometimes. Consider this, for example:

console.log(0 == '0');  // true
console.log(0 == '');   // true
console.log('' == '0'); // O'RLY?

... or this:

console.log(false == undefined); // false
console.log(false == null);      // false
console.log(null == undefined);  // fal.... NO WAIT!

...and that's exactly why it's almost always recommended to use === (strict equality) operator instead.