JavaScript Array.prototype.some()

JavaScript Array.prototype.some()
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The JavaScript array method .some() will take a callback function to test each element in the array; once the callback returns true then .some() will return true immediately.

Syntax

var arr = [1, 2, 3, 4];
arr.some(callback[, thisArg]);

Callback Function

Syntax

var isEven = function isEven(currentElement, index, array) {
    if(currentElement % 2 === 0) {
        return true;
    } else {
        return false;
    }
}

see wiki on Arithmetic Operators to see the remainder operator %

Has 3 arguments

  • currentElement

    • this is a variable that represents the element that is being passed to the callback.
  • index

    • this is the index value of the current element starting at 0
  • array

    • the array that .some() was call on.

The callback function should implement a test case.

thisArg

Is an optional parameter and more info can be found at the MDN

Description

.some() will run the callback function for each element in the array. Once the callback returns true, .some() will return true. If the callback returns a falsy value for every element in the array then .some() returns false.

.some() will not change/mutate the array that called it.

Examples

Passing a function to .some()

var isEven = function isEven(currentElement, index, array) {
    if(currentElement % 2 === 0) {
        return true;
    } else {
        return false;
    }
}

var arr1 = [1, 2, 3, 4, 5, 6];
arr1.some(isEven);  // returns true
var arr2 = [1, 3, 5, 7];
arr2.some(isEven);  // returns false

Anonymous function

var arr3 = ['Free', 'Code', 'Camp', 'The Amazing'];
arr3.some(function(curr, index, arr) {
    if (curr === 'The Amazing') {
        return true;
    } 
    }); // returns true

var arr4 = [1, 2, 14, 5, 17, 9];
arr4.some(function(curr, index, arr) {
    return curr > 20;
    });  // returns false

// ES6 arrows functions
arr4.some((curr) => curr >= 14)  // returns true

Source MDN


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