Check if array is empty or includes the value, typescript

Question

I check if array includes the value this way:

testArray.includes(value)

I need to do the same action if array is empty OR it includes the value. So I have this condition:

if (testArray == [] || testArray.includes(value)) {
    // do something
}

But typescript is trying to execute the second part of this condition even if testArray == []. So I receive an error testArray.includes is underfined.

I understand that I can fix it this way:

if (testArray == []) {
    // do something
} else if (testArray.includes(value)) {
    // do the same thing
}

But it doesn't look nice. Is there a way to put it in one if?

testArray is an openapi query parameter, if it's important.

`testArray == []` will always be false. See: [Why doesn't equality check work with arrays](https://stackoverflow.com/q/30820611) and [Why isn't \[1,2,3\] equal to itself in Javascript?](https://stackoverflow.com/q/7314635) Moreover, if you get `testArray.includes is underfined` then you don't have an empty array, you have some sort of value that is not an array. Likely an object. — VLAZ, Jul 19 '21 at 07:03

Majid M. · Accepted Answer · 2021-11-04T19:15:35.577

7

Acctually, array is a reference type. When you would like to check it with [ ], they aren't equal. They're totally different, it's better to check this condition with length. So based on your code you should do something like this :

if (!testArray || testArray.length == 0 || testArray.includes(value)) {
    // do something
}

edited Nov 04 '21 at 19:15

answered Jul 19 '21 at 07:02

Majid M.

4,467
1
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I tried it and it doesn't work too – `testArray. length is underfined` error – MarkBeras Jul 19 '21 at 07:20
Could you share your `testArray`'s items? I updated my code. Please try it again. – Majid M. Jul 19 '21 at 07:23

NotoriousPyro · Answer 2 · 2022-07-20T21:41:09.653

function isValueInArrayOrEmpty(updated) {
    console.log(Boolean(updated instanceof Array && (updated.length == 0 || (updated.length > 0 && updated.includes(value)))));
}
let value = "hello";
let updated = [];
isValueInArrayOrEmpty(updated);
let updated2 = "hello";
isValueInArrayOrEmpty(updated2);
let updated3 = Object;
isValueInArrayOrEmpty(updated3);
let updated4 = [Object];
isValueInArrayOrEmpty(updated4);
let updated5 = ["hello"];
isValueInArrayOrEmpty(updated5);
let updated6 = ["not hello"];
isValueInArrayOrEmpty(updated6);

VM815:2 true
VM815:2 false
VM815:2 false
VM815:2 false
VM815:2 true
VM815:2 false

score -1 · Answer 3 · answered Jul 19 '21 at 09:06

if (testArray == [] || testArray.includes(value)) { // do something }

In case of OR operator if the first condition is true it will skip rest all conditions. With that said your first condition testArray == [] is false , hence its executing the second part of condition. Probably your array is not empty array its having undefined value as it might not be initialized. Hence its throwing error.

Check if array is empty or includes the value, typescript

3 Answers3