Passing null as a param for replace() in javascript behaving weird?

Question

I have the follwing jQuery:

        $("#textArea").keyup(function(){
            var textAreaValue = $("textArea");
            if(!textArea.value.indexOf("some string")){
                textArea.value = textArea.value.replace("some string",null);
                alert("It was there!");
            }
        });

• Is it normal for element.value.replace("some string",null); to replace "some string" with "null"as a string? And if normal can you please explain why?

• I have tested it with element.value.replace("some string",""), and that works fine, so what would be the difference between null and ""?

Using FireFox 3.6.3, Thanks in advance.

Answer 1

"" is an empty string..

null is something that indicates a deliberate non-value or undefined...

null is mostly used to initialize objects

and in str.replace(param1,param2), param1 and param2 should be a string or something that produces a string ( in param2 )... in that said,

var heart_type = 'images/unheart.png';
alert( heart_type.replace(".png",null));​

will alert images/unheartnull.. because null was treated as a string...

.replace() reference

Answer 2

The second parameter of String.replace is a required parameter, and it must be a string. See mdc and w3schools. It's not normal or safe to pass null, which is not a string. Don't be surprised if your code does not execute properly in all javascript engines.

Answer 3

Seems like null has been type-casted to a String.

Try:

"a" + null // "anull"

Although you can't call toString() on a null object, it seems the null object is implicitly being converted to a String, which gives the string "null".

String(null) // "null"