Why "string" == ["string"] is true in JavaScript?

Question

I needed to iterate thought object and I'm losing my mind WIth this.

var obj = { a:"here", b: ["here"]};
for(var o in obj){
  alert(obj[o]=="here");
  }

Answer 1

The == operator will compare for equality after doing any necessary type conversions. The === operator will not do the conversion, so if two values are not the same type === will simply return false. It's this case where === will be faster, and may return a different result than ==. In all other cases performance will be the same.

It should be using === instead of ==:

var obj = { a:"here", b: ["here"]};
for(var o in obj){
  alert(obj[o]==="here");
  }

Answer 2

That's because you are comparing a string with an array by using the == operator. JavaScript interpreter converts the array into a string by calling the Array.prototype.toString method. The method calls the Array.prototype.join method behind the scenes.

["here"].toString() // => "here"
["here", "foo"].toString() // => "here,foo"