Updation in the body and code

[shivamrathi99]

URL(s)

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/some

Request type

• [ ] New documentation
• [ * ] Correction or update

Details

This below text is not clearly justifying the concept of "some" method in an array.

The some() method tests whether at least one element in the array passes the test implemented by the provided function. It returns a Boolean value. const array = [1, 2, 3, 4, 5];

// checks whether an element is even const even = (element) => element % 2 === 0;

console.log(array.some(even)); // expected output: true

it would improve the readability and will be easier to understand if it would be :

The some() method tests whether at least one element in the array passes the test implemented by the provided function. It returns a Boolean value. Some() does not mutate the array on which it is called.

const array = [1, 2, 3, 4, 5]; // checks whether an element is even const even = array.some(element => element % 2 === 0); console.log(even); // expected output: true

Thanks.

[RNabla]

Implementation of some does not modify, however provided callback could mutate array and tested objects. It's possible but it is asking for troubles. In my opinion using some should be idempotent - subsequent calls should have return the same test result.

"some does not directly mutate the object on which it is called but the object may be mutated by the calls to callbackfn." - Taken from https://tc39.es/ecma262/#sec-array.prototype.some

Here's example:

• callback modifies array
• it shows that item set is resolved before invoking callback - hence, why there's no infinite loop
• it shows that second calls returns different value - it's not idempotent

!(function () {
    const array = [1, 2, 3, 4];
    const callback = function (obj, index, arr) {
        if (obj === 42) {
            return true;
        }
        else if (obj % 2 === 0) {
            arr.push(42);
        }
        return false;
    };
    // [1, 2, 3, 4]
    console.log('Start:', JSON.parse(JSON.stringify(array)));
    // false
    console.log('Some: ', array.some(callback));
    // true
    console.log('Some: ', array.some(callback));
    // [1, 2, 3, 4, 42, 42]
    console.log('End', JSON.parse(JSON.stringify(array)));
})();

Please don't embed that on MDN, it's a bad code. However I would update description to be in sync with ECMAscript.

[shivamrathi99]

thanks for the explanation @RNabla

[chrisdavidmills]

Issue moved to mdn/content #1442 via ZenHub