TypedArray.prototype.findLastIndex()

findLastIndex()方法以相反顺序迭代类型化数组，并返回满足所提供测试函数的第一个元素的索引。如果没有值满足测试函数，则返回-1。

另请参阅findLast()方法，该方法返回找到的元素的值，而不是其索引。

语法

// Arrow function
findLastIndex((element) => { /* ... */ } )
findLastIndex((element, index) => { /* ... */ } )
findLastIndex((element, index, array) => { /* ... */ } )

// Callback function
findLastIndex(callbackFn)
findLastIndex(callbackFn, thisArg)

// Inline callback function
findLastIndex(function(element) { /* ... */ })
findLastIndex(function(element, index) { /* ... */ })
findLastIndex(function(element, index, array){ /* ... */ })
findLastIndex(function(element, index, array) { /* ... */ }, thisArg)

Parameters

A function used to test elements in the typed array.

The function is called with the following arguments:

The current element in the typed array.

The index(position)of the current element in the typed array.

The typed array thatfindLastIndex()was called on.

The callback must return a truthy value to indicate an appropriate element has been found. The index of this element is returned byfindLastIndex().

Object to use asthiswhen executingcallbackFn.

Return value

The index of the last(highest-index)element in the array that passes the test. Otherwise -1 if no matching element is found.

Description

ThefindLastIndex()method executes thecallbackFnfunction once for each index of the typed array in descending-index order until thecallbackFnreturns a truthy value.findLastIndex()then returns the index of that element and stops iterating through the typed array. IfcallbackFnnever returns a truthy value,findLastIndex()returnsundefined.

callbackFnis invoked with three arguments: the value of the element, the index of the element, and the typed array object being traversed.

If athisArgparameter is provided tofindLastIndex(), it will be used as thethisfor each invocation of thecallbackFn. If it is not provided, thenundefinedis used.

ThefindLastIndex()method does not mutate the typed array on which it is called, but the function provided tocallbackFncan.

The range of elements processed byfindLastIndex()is set before the first invocation ofcallbackFn. Elements that are appended to the typed array after the call tofindLastIndex()begins will not be visited bycallbackFn. If an existing, unvisited element of the typed array is changed bycallbackFn, its value passed to the visitingcallbackFnwill be the value at the time thatfindLastIndex()visits that element's index.

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).

实例

Find the index of a prime number in a typed array

The following example finds the index of the last element in the typed array that is a prime number(or returns-1if there is no prime number).

function isPrime(element) {
  if (element % 2 === 0 || element 

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