array.find

The find() method returns the value of the first element in the array that satisfies the provided testing function. Otherwise undefined is returned.

See also the findIndex() method, which returns the index of a found element in the array instead of its value.

If you need to find the position of an element or whether an element exists in an array, use Array.prototype.indexOf() or Array.prototype.includes().

Syntax

arr.find(callback[, thisArg])

Parameters

callback

Function to execute on each value in the array, taking three arguments:

element

The current element being processed in the array.

indexOptional

The index of the current element being processed in the array.

arrayOptional

The array find was called upon.

thisArg Optional

Object to use as this when executing callback.

Return value

A value in the array if an element passes the test; otherwise, undefined.

Description

The find method executes the callback function once for each index of the array until it finds one where callback returns a true value. If such an element is found, find immediately returns the value of that element. Otherwise, find returns undefined. callback is invoked for every index of the array from 0 to length - 1 and is invoked for all indexes, not just those that have been assigned values. This may mean that it's less efficient for sparse arrays than other methods that only visit indexes that have been assigned a value.

callback is invoked with three arguments: the value of the element, the index of the element, and the Array object being traversed.

If a thisArg parameter is provided to find, it will be used as the this for each invocation of the callback. If it is not provided, then undefined is used.

find does not mutate the array on which it is called.

The range of elements processed by find is set before the first invocation of callback. Elements that are appended to the array after the call to find begins will not be visited by callback. If an existing, unvisited element of the array is changed by callback, its value passed to the visiting callback will be the value at the time that find visits that element's index; elements that are deleted are still visited.

Examples

Find an object in an array by one of its properties

var inventory = [
    {name: 'apples', quantity: 2},
    {name: 'bananas', quantity: 0},
    {name: 'cherries', quantity: 5}
];

function isCherries(fruit) { 
    return fruit.name === 'cherries';
}

console.log(inventory.find(isCherries)); 
// { name: 'cherries', quantity: 5 }

Find a prime number in an array

The following example finds an element in the array that is a prime number (or returns undefined if there is no prime number).

function isPrime(element, index, array) {
  var start = 2;
  while (start <= Math.sqrt(element)) {
    if (element % start++ < 1) {
      return false;
    }
  }
  return element > 1;
}

console.log([4, 6, 8, 12].find(isPrime)); // undefined, not found
console.log([4, 5, 8, 12].find(isPrime)); // 5

The following examples show that non-existent and deleted elements are visited and that the value passed to the callback is their value when visited.

// Declare array with no element at index 2, 3 and 4
var a = [0,1,,,,5,6];

// Shows all indexes, not just those that have been assigned values
a.find(function(value, index) {
  console.log('Visited index ' + index + ' with value ' + value); 
});

// Shows all indexes, including deleted
a.find(function(value, index) {

  // Delete element 5 on first iteration
  if (index == 0) {
    console.log('Deleting a[5] with value ' + a[5]);
    delete a[5];
  }
  // Element 5 is still visited even though deleted
  console.log('Visited index ' + index + ' with value ' + value); 
});

Polyfill

This method has been added to the ECMAScript 2015 specification and may not be available in all JavaScript implementations yet. However, you can polyfill Array.prototype.find with the following snippet:

// https://tc39.github.io/ecma262/#sec-array.prototype.find
if (!Array.prototype.find) {
  Object.defineProperty(Array.prototype, 'find', {
    value: function(predicate) {
     // 1. Let O be ? ToObject(this value).
      if (this == null) {
        throw new TypeError('"this" is null or not defined');
      }

      var o = Object(this);

      // 2. Let len be ? ToLength(? Get(O, "length")).
      var len = o.length >>> 0;

      // 3. If IsCallable(predicate) is false, throw a TypeError exception.
      if (typeof predicate !== 'function') {
        throw new TypeError('predicate must be a function');
      }

      // 4. If thisArg was supplied, let T be thisArg; else let T be undefined.
      var thisArg = arguments[1];

      // 5. Let k be 0.
      var k = 0;

      // 6. Repeat, while k < len
      while (k < len) {
        // a. Let Pk be ! ToString(k).
        // b. Let kValue be ? Get(O, Pk).
        // c. Let testResult be ToBoolean(? Call(predicate, T, « kValue, k, O »)).
        // d. If testResult is true, return kValue.
        var kValue = o[k];
        if (predicate.call(thisArg, kValue, k, o)) {
          return kValue;
        }
        // e. Increase k by 1.
        k++;
      }

      // 7. Return undefined.
      return undefined;
    }
  });
}

If you need to support truly obsolete JavaScript engines that don't support Object.defineProperty, it's best not to polyfill Array.prototype methods at all, as you can't make them non-enumerable.

Specifications

Browser compatibility

See also

• Array.prototype.findIndex() – find and return an index
• Array.prototype.includes() – test whether a value exists in the array
• Array.prototype.filter() – find all matching elements
• Array.prototype.every() – test all elements together