偽數(shù)組轉(zhuǎn)為真數(shù)組

對(duì)DOM元素進(jìn)行map、forEach操作時(shí)候需要進(jìn)行遍歷，偽數(shù)組遍歷會(huì)報(bào)錯(cuò)：'elem.map is not a function',為了避免這個(gè)問(wèn)題，需要進(jìn)行轉(zhuǎn)換。

(1) ES5 轉(zhuǎn)為真數(shù)組

Array.prototype.slice.call(元素對(duì)象)

let elem1 = Array.prototype.slice.call(elem)

(2) ES6 轉(zhuǎn)為真數(shù)組

Array.from（元素對(duì)象）

let elem2 = Array.from(elem)

(3) 例子

<ul>
    <li class="a" ></li>
    <li class="a" ></li>
    <li class="a" ></li>
    <li class="a" ></li>
    <li class="a" ></li>
</ul>

<script>

/* 獲取li元素*/
let elem = document.getElementsByClassName('a')

/* 這樣寫(xiě)是錯(cuò)誤的,因?yàn)槭莻螖?shù)組*/
elem.map((item,index,elem) => {
    console.log(item +'---'+index + '----'+elem) 
    /*elem.map is not a function*/
})

// （1）es6 轉(zhuǎn)為真數(shù)組
let elem1 = Array.from(elem)
// （2）es5 轉(zhuǎn)為真數(shù)組
let elem2 = Array.prototype.slice.call(elem)

console.log(elem)
console.log(typeof elem)
console.log(elem1)
console.log(elem2)

elem1.map((item,index,elem1) => {
    console.log(item +'---'+index + '----'+elem1)
})
elem2.map((item,index,elem2) => {
    console.log(item +'---'+index + '----'+elem2)
})

</script>