JavaScript check if value is only undefined, null or false

Question

Other than creating a function, is there a shorter way to check if a value is undefined,null or false only in JavaScript?

The below if statement is equivalent to if(val===null && val===undefined val===false) The code works fine, I'm looking for a shorter equivalent.

if(val==null || val===false){
  ;
}

Above val==null evaluates to true both when val=undefined or val=null.

I was thinking maybe using bitwise operators, or some other trickery.

Solution 1

Well, you can always "give up" :)

function b(val){
    return (val==null || val===false);
}

Solution 2

The best way to do it I think is:

if(val != true){
//do something
} 

This will be true if val is false, NaN, or undefined.

Solution 3

I think what you're looking for is !!val==false which can be turned to !val (even shorter):

You see:

function checkValue(value) {
    console.log(!!value);
}

checkValue(); // false
checkValue(null); // false
checkValue(undefined); // false
checkValue(false); // false
checkValue(""); // false

checkValue(true); // true
checkValue({}); // true
checkValue("any string"); // true

That works by flipping the value by using the ! operator.

If you flip null once for example like so :

console.log(!null) // that would output --> true

If you flip it twice like so :

console.log(!!null) // that would output --> false

Same with undefined or false.

Your code:

if(val==null || val===false){
  ;
}

would then become:

if(!val) {
  ;
}

That would work for all cases even when there's a string but it's length is zero. Now if you want it to also work for the number 0 (which would become false if it was double flipped) then your if would become:

if(!val && val !== 0) {
  // code runs only when val == null, undefined, false, or empty string ""
}

Solution 4

One way to do it is like that:

var acceptable = {"undefined": 1, "boolean": 1, "object": 1};

if(!val && acceptable[typeof val]){
  // ...
}

I think it minimizes the number of operations given your restrictions making the check fast.

Solution 5

Another solution:

Based on the document, Boolean object will return true if the value is not 0, undefined, null, etc. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Boolean

If value is omitted or is 0, -0, null, false, NaN, undefined, or the empty string (""), the object has an initial value of false.

So

if(Boolean(val))
{
//executable...
}

View more solutions

Comments

[Joseph Marikle]

@missingno can't see why not... it's shorter than writing out if ... else ... and in any case, how shorter can you get a conditional statement like this? ... better answer than "just give up" imo >.>

[Rohan Desai]

All your conditional does is convert things to a boolean. However, this can be done much succintely with !! or, in this case, by doing nothing at all as the consition already is a boolean.

[Joseph Marikle]

@missingno no no no.... any code you want to execute based on the condition would go in place of the false and true... those are just there for clarity sake as to what results in what

[Felix Kling]

Some people consider this as bad style. The ternary operator should be used to return a value, not for it's side effects.

[Lime]

I would add functions where the false and true are then. Now it just appears as being over engineered.

[Lime]

Well I piratically gave up, but did end up changing false to !1

[Konza]

I think we can change val === false to val == false :)

[Rohan Desai]

@Konza: That just how == is defined. Its fairly complicated and its why many people recommend using === unless you really know what you are doing.

[Sam]

doesnot work better can be used as if(typeof variable_here === 'undefined'){ // your code here. };

[Felix Kling]

But that will also be true for 0 or "". Also, Yiding already provided this solution.

[TOPKAT]

It's crazy but for me it doesn't worw with null but with 'null' !! And also not work with val == '' (tested both in firefox console and live....if you have a clue ?

[Rohan Desai]

thats strange. you might want to create a separate question thread for that.

[Lime]

You forget 0 and ''

[SudoPlz]

Updated the answer to also take into account strings and the number zero 0.

[Lime]

This techique is probably the best disregarding the NaN value.

[JJS]

piratically - adv. do do something as pirate would...