TypedArray.prototype.findLast()

TypedArray 实例的 findLast() 方法以相反的顺序迭代类型化数组，并返回满足所提供的测试函数的第一个元素的值。如果没有元素满足测试功能，则返回 undefined。该方法与 Array.prototype.findLast() 的算法相同。

¥The findLast() method of TypedArray instances iterates the typed array in reverse order and returns the value of the first element that satisfies the provided testing function. If no elements satisfy the testing function, undefined is returned. This method has the same algorithm as Array.prototype.findLast().

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语法

¥Syntax

js
findLast(callbackFn)
findLast(callbackFn, thisArg)

参数

¥Parameters

callbackFn

对类型化数组中的每个元素执行的函数。它应该返回 truthy 值以指示已找到匹配元素，否则返回 falsy 值。使用以下参数调用该函数：

element

类型化数组中正在处理的当前元素。

index

类型化数组中当前正在处理的元素的索引。

array

调用了类型化数组 findLast()。

thisArg Optional

执行 callbackFn 时用作 this 的值。参见 迭代法。

返回值

¥Return value

类型化数组中满足所提供的测试函数的最后一个（最高索引）元素；如果未找到匹配元素，则返回 undefined。

¥The last (highest-index) element in the typed array that satisfies the provided testing function; undefined if no matching element is found.

描述

¥Description

详细信息请参见 Array.prototype.findLast()。此方法不是通用的，只能在类型化数组实例上调用。

¥See Array.prototype.findLast() for more details. This method is not generic and can only be called on typed array instances.

示例

¥Examples

查找类型化数组中的最后一个素数

¥Find the last prime number in a typed array

以下示例返回类型化数组中最后一个素数元素的值，如果没有素数，则返回 undefined。

¥The following example returns the value of the last element in the typed array that is a prime number, or undefined if there is no prime number.

js
function isPrime(element) {
  if (element % 2 === 0 || element < 2) {
    return false;
  }
  for (let factor = 3; factor <= Math.sqrt(element); factor += 2) {
    if (element % factor === 0) {
      return false;
    }
  }
  return true;
}

let uint8 = new Uint8Array([4, 6, 8, 12]);
console.log(uint8.findLast(isPrime)); // undefined (no primes in array)
uint8 = new Uint8Array([4, 5, 7, 8, 9, 11, 12]);
console.log(uint8.findLast(isPrime)); // 11

所有元素都被访问并且可以通过回调进行修改

¥All elements are visited and may be modified by the callback

以下示例显示所有元素都被访问，并且传递给回调的值是它们被访问时的值：

¥The following examples show that all elements are visited, and that the value passed to the callback is their value when visited:

js
// Declare array with no elements at indexes 2, 3, and 4
// The missing elements will be initialized to zero.
const uint8 = new Uint8Array([0, 1, , , , 5, 6]);

// Iterate through the elements in reverse order.
// Note that all elements are visited.
uint8.findLast((value, index) => {
  console.log(`Visited index ${index} with value ${value}`);
});

// Shows all indexes, including deleted
uint8.findLast((value, index) => {
  // Modify element 3 on first iteration
  if (index === 6) {
    console.log("Set uint8[3] to 44");
    uint8[3] = 44;
  }
  // Element 3 is still visited but will have a new value.
  console.log(`Visited index ${index} with value ${value}`);
});
// Visited index 6 with value 6
// Visited index 5 with value 5
// Visited index 4 with value 0
// Visited index 3 with value 0
// Visited index 2 with value 0
// Visited index 1 with value 1
// Visited index 0 with value 0
// Set uint8[3] to 44
// Visited index 6 with value 6
// Visited index 5 with value 5
// Visited index 4 with value 0
// Visited index 3 with value 44
// Visited index 2 with value 0
// Visited index 1 with value 1
// Visited index 0 with value 0

规范

Specification
ECMAScript Language Specification
# sec-%typedarray%.prototype.findlast

¥Specifications

浏览器兼容性

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¥Browser compatibility

也可以看看

¥See also