什么是通过一组在JavaScript中的元素循环的最佳方式? [英] What's the best way to loop through a set of elements in JavaScript?
问题描述
在过去,大多数我目前的项目我倾向于使用一个像这样的循环:
VAR元素= document.getElementsByTagName('DIV');
对于(VAR I = 0; I< elements.length;我++){
DoSomething的(元素[I]);
}
我听说用的是逆向而循环更快,但我没有真正的方法来证实这一点:
VAR元素= document.getElementsByTagName('DIV'),
长度= elements.length;而(length--){
DoSomething的(元素[长度]);
}
什么被认为是最好的做法,当涉及到循环尽管在JavaScript元素,或与此有关的任何阵列?
下面是一个循环我经常使用的一个很好的形式。创建从for语句迭代变量,你不需要检查length属性,通过迭代的NodeList时,它可以是昂贵的特制。然而,您必须小心,您不能使用它,如果任何在阵列中的值可以是falsy。在实践中,我只遍历一个不包含空值(如节点列表)对象的数组时使用它。但我喜欢它的语法糖。
VAR名单= [{A:1,B:2},{一:3,B:5},{A:8,B:2},{A:4 ,b:1},{一个:0,b:8}];对于(VAR I = 0,项;项目=列表[我]我++){
//你看没必要做的循环体名单[I]
的console.log(循环:指数,我,项+项目);
}
请注意,这也可以被用来循环向后(只要你的列表中不具有 [' - 1']
属性)
VAR名单= [{A:1,B:2},{A: 3,b:5},{A:8,b:2},{A:4,b:1},{A:0,b:8}];\r
\r
对于(VAR I = List.length的数字 - 1项;项目=列表[我];我 - ){\r
的console.log(循环:指数,我,项目,项目);\r
}
\r
In the past and with most my current projects I tend to use a for loop like this:
var elements = document.getElementsByTagName('div');
for (var i=0; i<elements.length; i++) {
doSomething(elements[i]);
}
I've heard that using a "reverse while" loop is quicker but I have no real way to confirm this:
var elements = document.getElementsByTagName('div'),
length = elements.length;
while(length--) {
doSomething(elements[length]);
}
What is considered as best practice when it comes to looping though elements in JavaScript, or any array for that matter?
Here's a nice form of a loop I often use. You create the iterated variable from the for statement and you don't need to check the length property, which can be expensive specially when iterating through a NodeList. However, you must be careful, you can't use it if any of the values in array could be "falsy". In practice, I only use it when iterating over an array of objects that does not contain nulls (like a NodeList). But I love its syntactic sugar.
var list = [{a:1,b:2}, {a:3,b:5}, {a:8,b:2}, {a:4,b:1}, {a:0,b:8}];
for (var i=0, item; item = list[i]; i++) {
// Look no need to do list[i] in the body of the loop
console.log("Looping: index ", i, "item" + item);
}
Note that this can also be used to loop backwards (as long as your list doesn't have a ['-1']
property)
var list = [{a:1,b:2}, {a:3,b:5}, {a:8,b:2}, {a:4,b:1}, {a:0,b:8}];
for (var i = list.length - 1, item; item = list[i]; i--) {
console.log("Looping: index ", i, "item", item);
}
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