在此页

• 句法
• 描述
• Polyfill
• 范例
• 规范
• 浏览器兼容性
• 另请参阅
• 相关话题

findIndex() method returns the index of the first element in the array that satisfies the provided testing function . Otherwise, it returns -1 , indicating that no element passed the test.

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.

另请参阅 find() method, which returns the value of an array element, instead of its index.

句法

arr.findIndex(callback( element[, index[, array]] )[, thisArg])
				

参数

callback

A function to execute on each value in the array until the function returns true , indicating that the satisfying element was found.

It takes three arguments:

element

The current element being processed in the array.

index 可选

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

array 可选

The array findIndex() was called upon.

thisArg 可选

Optional object to use as this when executing callback .

返回值

The index of the first element in the array that passes the test. Otherwise, -1 .

描述

findIndex() method executes the callback function once for every index in the array until it finds the one where callback 返回 truthy 值。

If such an element is found, findIndex() immediately returns the element's index. If callback never returns a truthy value (or the array's length is 0 ), findIndex() 返回 -1 .

Edge case alert: Unlike other array methods such as Array.some() , callback is run even for indexes with unassigned values.

callback is invoked with three arguments:

1. The value of the element
2. The index of the element
3. The Array object being traversed

若 thisArg parameter is passed to findIndex() , it will be used as the this inside each invocation of the callback . If it is not provided, then undefined 被使用。

The range of elements processed by findIndex() is set before the first invocation of callback . callback will not process the elements appended to the array after the call to findIndex() begins. If an existing, unvisited element of the array is changed by callback , its value passed to the callback will be the value at the time findIndex() visits the element's index.

Elements that are deleted are still visited.

Polyfill

// https://tc39.github.io/ecma262/#sec-array.prototype.findindex
if (!Array.prototype.findIndex) {
  Object.defineProperty(Array.prototype, 'findIndex', {
    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 k.
        var kValue = o[k];
        if (predicate.call(thisArg, kValue, k, o)) {
          return k;
        }
        // e. Increase k by 1.
        k++;
      }
      // 7. Return -1.
      return -1;
    },
    configurable: true,
    writable: true
  });
}
						

If you need to support truly obsolete JavaScript engines that do not support Object.defineProperty , it is best not to polyfill Array.prototype methods at all, as you cannot make them non-enumerable.

范例

Find the index of a prime number in an array

The following example returns the index of the first element in the array that is a prime number, or -1 if there is no prime number.

function isPrime(num) {
  for (let i = 2; num > i; i++) {
    if (num % i == 0) {
      return false;
    }
  }
  return num > 1;
}
console.log([4, 6, 8, 9, 12].findIndex(isPrime)); // -1, not found
console.log([4, 6, 7, 9, 12].findIndex(isPrime)); // 2 (array[2] is 7)
						

Find index using arrow function

The following example finds the index of a fruit using an arrow function:

const fruits = ["apple", "banana", "cantaloupe", "blueberries", "grapefruit"];
const index = fruits.findIndex(fruit => fruit === "blueberries");
console.log(index); // 3
console.log(fruits[index]); // blueberries
						

规范

规范
ECMAScript (ECMA-262) The definition of 'Array.prototype.findIndex' in that specification.

浏览器兼容性

The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 更新 GitHub 上的兼容性数据

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
findIndex	Chrome 45	Edge 12	Firefox 25	IE No	Opera 32	Safari 8	WebView Android 45	Chrome Android 45	Firefox Android 4	Opera Android 32	Safari iOS 8	Samsung Internet Android 5.0	nodejs 4.0.0 4.0.0 0.12 Disabled Disabled From version 0.12: this feature is behind the --harmony runtime flag.

图例

完整支持

完整支持

不支持

不支持

用户必须明确启用此特征。

用户必须明确启用此特征。

另请参阅

• Array.prototype.find()
• Array.prototype.indexOf()

元数据

• 最后修改： May 31, 2020

相关话题

1. 标准内置对象
2. Array
3. 特性
   1. Array.prototype.length
   2. Array.prototype[@@unscopables]
4. 方法
   1. Array.from()
   2. Array.isArray()
   3. Array.of()
   4. Array.prototype.concat()
   5. Array.prototype.copyWithin()
   6. Array.prototype.entries()
   7. Array.prototype.every()
   8. Array.prototype.fill()
   9. Array.prototype.filter()
   10. Array.prototype.find()
   11. Array.prototype.findIndex()
   12. Array.prototype.flat()
   13. Array.prototype.flatMap()
   14. Array.prototype.forEach()
   15. Array.prototype.includes()
   16. Array.prototype.indexOf()
   17. Array.prototype.join()
   18. Array.prototype.keys()
   19. Array.prototype.lastIndexOf()
   20. Array.prototype.map()
   21. Array.prototype.pop()
   22. Array.prototype.push()
   23. Array.prototype.reduce()
   24. Array.prototype.reduceRight()
   25. Array.prototype.reverse()
   26. Array.prototype.shift()
   27. Array.prototype.slice()
   28. Array.prototype.some()
   29. Array.prototype.sort()
   30. Array.prototype.splice()
   31. Array.prototype.toLocaleString()
   32. Array.prototype.toSource()
   33. Array.prototype.toString()
   34. Array.prototype.unshift()
   35. Array.prototype.values()
   36. Array.prototype[@@iterator]()
   37. get Array[@@species]
5. 继承：
6. Function
7. 特性
   1. Function.arguments
   2. Function.caller
   3. Function.displayName
   4. Function.length
   5. Function.name
8. 方法
   1. Function.prototype.apply()
   2. Function.prototype.bind()
   3. Function.prototype.call()
   4. Function.prototype.toSource()
   5. Function.prototype.toString()
9. Object
10. 特性
    1. Object.prototype.__proto__
    2. Object.prototype.constructor
11. 方法
    1. Object.prototype.__defineGetter__()
    2. Object.prototype.__defineSetter__()
    3. Object.prototype.__lookupGetter__()
    4. Object.prototype.__lookupSetter__()
    5. Object.prototype.hasOwnProperty()
    6. Object.prototype.isPrototypeOf()
    7. Object.prototype.propertyIsEnumerable()
    8. Object.prototype.toLocaleString()
    9. Object.prototype.toSource()
    10. Object.prototype.toString()
    11. Object.prototype.valueOf()
    12. Object.setPrototypeOf()