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? — Subodh Joshi
– Subodh Joshi, Commented Jul 24, 2015 at 7:42
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
– T.J. Crowder, Commented Jul 24, 2015 at 7:47
@SubodhJoshi: No, that matches the title of this question, but not the content. — T.J. Crowder
– T.J. Crowder, Commented Jul 24, 2015 at 7:48
@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
– T.J. Crowder, Commented Jul 24, 2015 at 7:51

T.J. Crowder · Accepted Answer · 2015-07-24 07:52:53Z

4

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.

edited Jul 24, 2015 at 7:52

answered Jul 24, 2015 at 7:45

T.J. Crowder

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