shortcut to check if variable is null || undefined||empty string||false

Question

I am looking for check, if my variable is one of : null || undefined || empty string || false

Right now its look messy and long:

const userHasPhoneNumber = user.phone === undefined || 
                           user.phone === "" || 
                           user.phone === false ||
                           user.phone === null ? false : true;

Is there shortcut?

What kind of data is this, where it's completely valid, to have a phone number be any one of these? Something doesn't seem right here. — ASDFGerte, Dec 22 '20 at 15:11

Ricola · Answer 1 · 2020-12-22T15:15:07.360

If you coerce that string to a boolean then it should check all your conditions, which is pretty much checking if user.phone is truthy.

It depends how you want to use it. If you wanted to use it in a condition, i.e. if(userHasPhoneNumber) ... then you can use the string directly : if(user.phone) as it will coerce to a boolean.

If you really need to have a boolean variable then need to cast it to a boolean explicitely:

Either through const userHasPhoneNumber = Boolean(user.phone); or const userHasPhoneNumber = !!user.phone;

Note, as @Bergi commented, that there are more values that are coerced to a false value (falsy values), for example NaN or the number 0 (the string "0" will coerce to true), so it depends what your input is. If it's never a number but either a string/boolean/null/undefined, it should be fine. Here is the list of all falsy values for reference : https://developer.mozilla.org/en-US/docs/Glossary/Falsy

Different result for `0` and `NaN` – Bergi Dec 22 '20 at 15:07 — Bergi, Dec 22 '20 at 15:07
Thank. Take a look in my comment for 0stone0 – Roei Grinshpan Dec 22 '20 at 16:25 — Roei Grinshpan, Dec 22 '20 at 16:25

score 1 · Answer 2 · answered Dec 22 '20 at 15:11

1

You can shortcut x === undefined || x === null to x == null. For the others, there is no shortcut as there are some falsy number values as well. You could however do

const userHasPhoneNumber = typeof user.phone == "number" || !!user.phone

answered Dec 22 '20 at 15:11

Bergi

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simple and elegant – Peter Seliger Dec 22 '20 at 15:17

0stone0 · Answer 3 · 2020-12-22T15:17:45.897

1

Use JavaScript's !!, witch will become false for null, "", undefined and false:

const user = {
  phone_1: null,
  phone_2: "",
  phone_3: undefined,
  phone_4: false
};

console.log(!!user.phone_1);  // false
console.log(!!user.phone_2);  // false
console.log(!!user.phone_3);  // false
console.log(!!user.phone_4);  // false

Note Use this with caution as some results may be different then expected, this answer shows a complete list.

edited Dec 22 '20 at 15:17

answered Dec 22 '20 at 15:13

0stone0

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…but also for some other values. – Bergi Dec 22 '20 at 15:14
Thabk u. My phone variables has checked before so je can be only undefined or empty or if user enter phone so it already a number of length 10 exactly – Roei Grinshpan Dec 22 '20 at 16:24
This function hasPHonenumber that i mentioned is for show modal if user dont have phone number – Roei Grinshpan Dec 22 '20 at 16:25

shortcut to check if variable is null || undefined||empty string||false

3 Answers3