In Javascript, == “” evaluates to true. Why is it so?

Question

If I do 0 == \"0\" it evaluates to true. Try,

if( -777 == \"-777\" ) alert(\"same\");

alert happens.

And, it\'s also noticeable th

Answer 1

Because Javascript is loosely typed, it will silently cast your variables depending on the operation and the type of the other variables in the operation.

alert ("5" - 1);  // 4  (int)
alert ("5" + 1);  // "51" (string) "+" is a string operator, too
alert ("5" == 5); // true

What you might want to look at is identity checking (===). That makes sure the variables are identical, not merely equal.

alert("5" == 5);  // true, these are equal
alert("5" === 5); // false, these are not identical.

Also see this question: How do the equality and identity comparison operators differ? PHP's implementation is very similar to javascript's.