javascript check for not null

There are 3 ways to check for "not null". My recommendation is to use the Strict Not Version.

1. Strict Not Version

if (val !== null) { ... }

The Strict Not Version uses the "Strict Equality Comparison Algorithm" http://www.ecma-international.org/ecma-262/5.1/#sec-11.9.6. The !== has faster performance, than the != operator because the Strict Equality Comparison Algorithm doesn't typecast values.

2. Non-strict Not Version

if (val != 'null') { ... }

The Non-strict version uses the "Abstract Equality Comparison Algorithm" http://www.ecma-international.org/ecma-262/5.1/#sec-11.9.3. The != has slower performance, than the !== operator because the Abstract Equality Comparison Algorithm typecasts values.

3. Double Not Version

if (!!val) { ... }

The Double Not Version !! has faster performance, than both the Strict Not Version !== and the Non-Strict Not Version != (https://jsperf.com/tfm-not-null/6). However, it will typecast "Falsey" values like undefined and NaN into False (http://www.ecma-international.org/ecma-262/5.1/#sec-9.2) which may lead to unexpected results, and it has worse readability because null isn't explicitly stated.

this will do the trick for you

if (!!val) {
    alert("this is not null")
} else {
    alert("this is null")
}