how to check null in javascript?

Question

var someValue1 = '${requestScope.someValue}';
    var someValue = '${requestScope.someValue}';
    var someValue = '${requestScope.someValue}';
    if(someValue1 !== null && someValue1 !== undefined && someValue1 !== '' && someValue1!=='null'){
        alert('Your New someValue1 = '+someValue1);
    };
    if(someValue !== null && someValue !== undefined && someValue !== '' && someValue!=='null' ){
        alert('Error : ' + someValue +"\nDescription : " + someValue);
    };

i want to execute only one alert box depending on the values but null checking is not working.

My both alert boxes are getting executed and that is my main problem. i cant understand why.

possible duplicate of [How do I check for null values in javascript?](http://stackoverflow.com/questions/6003884/how-do-i-check-for-null-values-in-javascript) — Subodh Joshi, Jul 24 '15 at 07:42
Do you have something processing those `'{$requestScope.someValue}'` string literals in some way? Because in your code above, you have the actual string `'{$requestScope.someValue}'`. — T.J. Crowder, Jul 24 '15 at 07:47
@SubodhJoshi: No, that matches the title of this question, but not the content. — T.J. Crowder, Jul 24 '15 at 07:48
@tushargarg: Then that's your problem, it's exactly like `var someValue = 'foo';`. The value you're checking is the actual string `'{$requestScope.someValue}`. — T.J. Crowder, Jul 24 '15 at 07:51

T.J. Crowder · Answer 1 · 2015-07-24T07:52:53.523

All of your values are strings, because you've put them in quotes:

var someValue1 = '${requestScope.someValue}';
// --------------^-------------------------^

Consequently, they'll never be === null or === undefined. Moreover, unless you have something processing those that you haven't shown, they'll never be === '', either, because they're the literal string {$requestScope.someValue} (exactly like 'foo' is the literal string foo).

If you want to check the value, check the value itself, requestScope.someValue.

how to check null in javascript?

1 Answers1