How to check if a variable is not null?

Question

I know that below are the two ways in JavaScript to check whether a variable is not null, but I’m confused which is the best practice to use.

Should I d

Answer 1

if (0) means false, if (-1, or any other number than 0) means true. following value are not truthy, null, undefined, 0, ""empty string, false, NaN

never use number type like id as

      if (id) {}

for id type with possible value 0, we can not use if (id) {}, because if (0) will means false, invalid, which we want it means valid as true id number.

So for id type, we must use following:

   if ((Id !== undefined) && (Id !== null) && (Id !== "")){
                                                                                
                                                                            } else {

                                                                            }
                                                                            

for other string type, we can use if (string) {}, because null, undefined, empty string all will evaluate at false, which is correct.

       if (string_type_variable) { }

Answer 2

if myVar is null then if block not execute other-wise it will execute.

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

Answer 3

• code inside your if(myVar) { code } will be NOT executed only when myVar is equal to: false, 0, "", null, undefined, NaN or you never defined variable myVar (then additionally code stop execution and throw exception).
• code inside your if(myVar !== null) {code} will be NOT executed only when myVar is equal to null or you never defined it (throws exception).

Here you have all (src)

if

== (its negation !=)

=== (its negation !==)