Array.prototype.find()

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

The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

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(element[, index[, array]])[, thisArg])

Parameters

callback

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

element

The current element being processed in the array.

index Optional

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

array Optional

The array find was called upon.

thisArg Optional

Optional object to use as this when executing callback.

Return value

The value of the first element in the array that satisfies the provided testing function. Otherwise, undefined is returned.

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 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 it is invoked for all indexes, not just those that have been assigned values. This indicates that it may be less efficient for sparse arrays compared to other methods that only visit indexes with assigned 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 value for each invocation of the callback. If it is not provided, then undefined is used.

The find method 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. Therefore, callback will not visit the elements that are appended to the array after the call to find begins. If an existing, unvisited element of the array is changed by callback, its value passed to the callback will be the given value at the time 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 }

Using ES2015 arrow function

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

const result = inventory.find( fruit => fruit.name === 'cherries' );

console.log(result) // { 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 array = [0,1,,,,5,6];

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

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

  // Delete element 5 on first iteration
  if (index == 0) {
    console.log('Deleting array[5] with value ' + array[5]);
    delete array[5];
  }
  // Element 5 is still visited even though deleted
  console.log('Visited index ' + index + ' with value ' + value); 
});
// expected output:
// Deleting array[5] with value 5 
// Visited index 0 with value 0 
// Visited index 1 with value 1 
// Visited index 2 with value undefined 
// Visited index 3 with value undefined 
// Visited index 4 with value undefined 
// Visited index 5 with value undefined 
// Visited index 6 with value 6

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;
    },
    configurable: true,
    writable: true
  });
}

If you need to support truly obsolete JavaScript engines that don't support Object.defineProperty, it is best not to polyfill Array.prototype methods at all, as you cannot 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
• Array.prototype.some() – test at least one element