javascript - How to check a null value with an extension method using Object.prototype - Stack Overflow

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There are a variety of places where I need to check if a JavaScript variable is null or empty string so I wrote an extension method that looks like this:

Object.prototype.IsNullOrEmptyString = function()
{
    return (this == null || (typeof this === "string" && this.length == 0));
}

I then call it like so:

var someVariable = null;

if (someVariable.IsNullOrEmptyString())
    alert("do something");

But that doesn't work because, at the point of evaluation in the if statement, someVariable is null. The error I keep getting is "someVariable is null".

You can see it live here: / (run in Firefox and notice the error console)

Is there anyway to do what I want and have a single extension method check for null and other things at the same time?

There are a variety of places where I need to check if a JavaScript variable is null or empty string so I wrote an extension method that looks like this:

Object.prototype.IsNullOrEmptyString = function()
{
    return (this == null || (typeof this === "string" && this.length == 0));
}

I then call it like so:

var someVariable = null;

if (someVariable.IsNullOrEmptyString())
    alert("do something");

But that doesn't work because, at the point of evaluation in the if statement, someVariable is null. The error I keep getting is "someVariable is null".

You can see it live here: http://jsfiddle/AhnkF/ (run in Firefox and notice the error console)

Is there anyway to do what I want and have a single extension method check for null and other things at the same time?

• javascript

Share Improve this question Follow asked Nov 3, 2011 at 15:17 sohtimsso1970sohtimsso1970 3,28655 gold badges3030 silver badges3939 bronze badges 1

• Extending Object is not a good idea. It should be considered "final" – Bakudan Commented Nov 3, 2011 at 15:40

Add a ment  | 

3 Answers 3

Sorted by: Reset to default 3

null does not have any properties or methods. You have to create a function, and pass the variable, so it can be tested. Note: To test whether a variable is really an empty string, using === "" is remended.^*

function isNullOrEmpty(test) {
    return test === null || test === "";
}

var someVariable = null;
if (isNullOrEmpty(someVariable)) alert("Do something");

^* about == and ===. The following parisons are true:

null == undefined
"" == 0;
"" == false
"" == 

Because your variable is not an object, so its not working. Do it this way.

Object.prototype.IsNullOrEmptyString = function(obj)
{
    return (obj == null || (typeof this === "string" && this.length == 0));
}


if(Object.IsNullOrEmptyString(null))
  alert('yes');

just make it a function call.

function IsEmptyString(value)
{
    return (value == null ||
            value === "");
}

Here is a fiddle

Edit: consolidated (=== undefined and === null) into (== null)

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