Check if All Array Items Are Equal in JavaScript

December 12, 2021 - 1 minute read

The following JavaScript function returns true if each item in the passed array is of a matching type and value:

// Same value, same type
const isUniform = (array) => {
    const firstItem = array[0];
    return array.every((item) => item === firstItem);
};

isUniform([`a`, `b`, `c`]); // returns false

isUniform([`a`, `a`, `a`]); // returns true

Otherwise, it returns false.

And the following modified isUniform function serves the same function, except it does not check for matching types, and only checks for matching values:

// Same value, arbitrary type
const isUniform = (array) => {
    const firstItem = array[0];
    return array.every((item) => item == firstItem);
};

isUniform([`1`, 2, 3]); // returns false

isUniform([1, 2, 3]); // returns false

isUniform([`1`, 1, 1]); // returns true

isUniform([1, 1, 1]); // returns true

The only difference between the above two snippets is the equality operators used in the every() array method, which performs the same test on each item in a given array.

Conclusion

This is the quickest and simplest way I’ve found to check whether every item in a JavaScript array is of the same value. I hope it helps you out!

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Conclusion