如何获取数组原型图中的当前索引? [英] How to get current index in Array prototype map?

问题描述

我正在使用 Array.prototype.map.call 将一堆节点列表对象存储在一个数组中:

I'm using Array.prototype.map.call to store in an array a bunch of node list objects:

function getListings() {
    return Array.prototype.map.call(document.querySelectorAll('li.g'), function(e) {
         return {
             rectangle: e.getBoundingClientRect();
         }
    }
}

但是，我也想存储这个元素在DOM中出现的顺序，不知道怎么做.

However, I also want to store the order in which this elements appear in the DOM, and I don't know how to do that.

我知道我将它存储在一个数组中，顺序将是数组的索引.例如:

I know that I'm storing this in an array, and the order would be the index of the array. For example:

var listings = getListings();
console.log(listings[0]); // rank #1
console.log(listings[1]); // rank #2
// etc...

但是我在数据库中插入了 json 对象，存储rank"信息的最简单方法是在我的对象中创建一个属性rank"，但我不知道如何获取index""的当前数组.

but I'm inserting the json object in a database, and the easiest way to store the "rank" information is by creating a property "rank" in my object, but I don't know how to get the "index" of the current array.

类似于:

function getListings() {
    return Array.prototype.map.call(document.querySelectorAll('li.g'), function(e) {
         return {
             rectangle: e.getBoundingClientRect(),
             rank: magicFunctionThatReturnsCurrentIndex() // <-- magic happens
         }
    }
}

任何为我指明正确方向的帮助将不胜感激！谢谢

Any help pointing me to the right direction will be greatly appreciated! Thanks

推荐答案

MDN 文档 说:

callback 使用三个参数调用:元素的值，元素的索引，以及被遍历的 Array 对象.

callback is invoked with three arguments: the value of the element, the index of the element, and the Array object being traversed.

所以

function getListings() {
    return Array.prototype.map.call(document.querySelectorAll('li.g'), function(e, rank) { // magic 
         return {
             rectangle: e.getBoundingClientRect(),
             rank: rank // <-- magic happens
         }
    }
}

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