The find() method returns the first element in the provided array that satisfies the provided testing function. If no values satisfy the testing function, undefined is returned. Try it
Syntax
// Arrow function find((element) => { /* … */ } ) find((element, index) => { /* … */ } ) find((element, index, array) => { /* … */ } ) // Callback function find(callbackFn) find(callbackFn, thisArg) // Inline callback function find(function(element) { /* … */ }) find(function(element, index) { /* … */ }) find(function(element, index, array){ /* … */ }) find(function(element, index, array) { /* … */ }, thisArg)
Parameters
callbackFn
Function to execute on each value in the array.
The function is called with the following arguments:
elementThe current element in the array.
indexThe index (position) of the current element in the array.
arrayThe array that find was called on.
The callback must return a truthy value to indicate a matching element has been found.
thisArg OptionalObject to use as this inside callbackFn.
Return value
The first element in the array that satisfies the provided testing function. Otherwise, undefined is returned.
Description
The find method executes the callbackFn function once for each index of the array until the callbackFn returns a truthy value. If so, find immediately returns the value of that element. Otherwise, find returns undefined.
callbackFn is invoked for every index of the array, not just those with assigned values. This means it may be less efficient for sparse arrays, compared to methods that only visit assigned values.
If a thisArg parameter is provided to find, it will be used as the this value inside each invocation of the callbackFn. If it is not provided, then undefined is used.
The find method does not mutate the array on which it is called, but the function provided to callbackFn can. If so, the elements processed by find are set before the first invocation of callbackFn. Therefore:
- callbackFn will not visit any elements added to the array after the call to find begins.
- Elements which are assigned to indexes already visited, or to indexes outside the range, will not be visited by callbackFn.
- If an existing, yet-unvisited element of the array is changed by callbackFn, its value passed to the callbackFn will be the value at the time find visits that element's index.
- Elements that are deleted are still visited.
Warning: Concurrent modification of the kind described in the previous paragraph frequently leads to hard-to-understand code and is generally to be avoided (except in special cases).
Examples
Find an object in an array by one of its properties
const 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 arrow function and destructuring
const inventory = [ {name: 'apples', quantity: 2}, {name: 'bananas', quantity: 0}, {name: 'cherries', quantity: 5} ]; const result = inventory.find(({ name }) => 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) { let 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 nonexistent and deleted elements are visited, and that the value passed to the callback is their value when visited:
// Declare array with no elements at indexes 2, 3, and 4 const array = [0,1,,,,5,6]; // Shows all indexes, not just those with assigned values array.find((value, index) => { console.log('Visited index ', index, ' with value ', value); }); // Shows all indexes, including deleted array.find((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: // 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 5 // Visited index 6 with value 6 // 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
Specifications
ECMAScript Language Specification # sec-array.prototype.find |
Browser compatibility
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