[英]Javascript Efficiency Question: multiple getElementById() vs getElementsByTagName() and looping through result
[英]Looping through JavaScript "getElementsByTagName()" object
如何正確循環從選擇器上的“getElementsByTagName()”返回的對象。 我似乎無法正確處理。
例如,如果我有一堆這樣的 div:
<div class="wrapper">
<div class="test1">this is a div</div>
<div class="test2">this is a div</div>
<div class="test1">this is a div</div>
<div class="test2">this is a div</div>
<div class="test1">this is a div</div>
<div class="test2">this is a div</div>
</div>
我想遍歷“getElementsByTagName()”的結果,如下所示:
var wrapper = document.querySelector(".wrapper");
var divs = wrapper.getElementsByTagName("div");
for (i = 0; i < divs.length; ++i) {
each = divs[i];
if (each.classList.contains("test2")) {
this.style.display = "none";
}
}
這是一個小提琴: http : //jsfiddle.net/Y2Yzv/1/
控制台中有錯誤: Uncaught TypeError: Cannot set property 'display' of undefined
嘗試:
var wrapper = document.querySelector(".wrapper");
var divs = wrapper.getElementsByTagName("div");
for (i = 0; i < divs.length; ++i) {
each = divs[i];
if (each.classList.contains("test2")) {
each.style.display = "none";
}
}
each.style.display = "none";
會工作而不是this
this
指的是全局對象,而不是循環中迭代的元素。
這是糾正的小提琴:
更少代碼解決方案
var divs = document.querySelectorAll('.wrapper div');
[].forEach.call(divs, function (div) {
if (div.classList.contains('test2')) div.style.display = 'none';
});
改變this.style.display = "none";
to each.style.display = "none"
檢查此解決方案: http : //jsfiddle.net/ZffWg/
這些是我改變的主要變化
for (i in divs) {
if (divs[i].className.indexOf("test2") > -1) {
divs[i].style.display = "none";
}
}
我刪除了i=0
,因此循環在數組索引本身上運行。
我還使用className
而不是classList
來實現更好的跨平台兼容性
let divs_in_wrapper = document.querySelectorAll('.wrapper div'); divs_in_wrapper.forEach((item, index, arr) => { if (item.classList.contains("test2")) { item.style.display = "none"; } });
<div class="wrapper"> <div class="test1">this is a div</div> <div class="test2">this is a div class test2</div> <div class="test1">this is a div</div> <div class="test2">this is a div class test2</div> <div class="test1">this is a div</div> <div class="test2">this is a div class test2</div> </div> <div class="test2">this is outside a div</div>
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