How to use JavaScript Array.prototype.some() - JavaScript Some Guide

How to use JavaScript Array.prototype.some() - JavaScript Some Guide
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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
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