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 and Why isn't [1,2,3] equal to itself in Javascript? 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
– VLAZ, Commented Jul 19, 2021 at 7:03

Majid M. · Accepted Answer · 2023-10-18 06:59:44Z

10

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

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

edited Oct 18, 2023 at 6:59

answered Jul 19, 2021 at 7:02

Majid M.

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2 Comments

MarkBeras Over a year ago

I tried it and it doesn't work too – testArray. length is underfined error

Majid M. Over a year ago

Could you share your testArray's items? I updated my code. Please try it again.

NotoriousPyro · Accepted Answer · 2022-07-20 21:41:09Z

0

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

edited Jul 20, 2022 at 21:41

answered Jul 19, 2022 at 23:51

NotoriousPyro

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Comments

Anjali Sharma · Accepted Answer · 2021-07-19 09:06:55Z

-2

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.

answered Jul 19, 2021 at 9:06

Anjali Sharma

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