if-else、switch 或 map based 条件的性能

Performance of if-else, switch or map based conditioning(if-else、switch 或 map based 条件的性能)

问题描述

我想知道以下 javascript 中条件结构的实现的性能.

I was wondering about the performances of the following implementations of conditional structs in javascript.

方法一:

 if(id==="camelCase"){
    window.location.href = "http://www.thecamelcase.com";
}else if (id==="jsFiddle"){
    window.location.href = "http://jsfiddle.net/";
}else if (id==="cricInfo"){
    window.location.href = "http://cricinfo.com/";
}else if (id==="apple"){
    window.location.href = "http://apple.com/";
}else if (id==="yahoo"){
    window.location.href = "http://yahoo.com/";
}           

方法二:

switch (id) {
case 'camelCase':
    window.location.href = "http://www.thecamelcase.com";
    break;
case 'jsFiddle':
    window.location.href = "http://www.jsfiddle.net";
    break;
case 'cricInfo':
    window.location.href = "http://www.cricinfo.com";
    break;
case 'apple':
    window.location.href = "http://www.apple.com";
    break;
case 'yahoo':
    window.location.href = "http://www.yahoo.com";
    break;

}

方法3

var hrefMap = {
camelCase : "http://www.thecamelcase.com",
jsFiddle: "http://www.jsfiddle.net",
cricInfo: "http://www.cricinfo.com",
apple: "http://www.apple.com",
yahoo: "http://www.yahoo.com"
};
window.location.href = hrefMap[id];

方法四

window.location.href = {
    camelCase : "http://www.thecamelcase.com",
    jsFiddle: "http://www.jsfiddle.net",
    cricInfo: "http://www.cricinfo.com",
    apple: "http://www.apple.com",
    yahoo: "http://www.yahoo.com"
}[id];

可能方法 3 和 4 可能具有几乎相同的性能，但只是发布以确认.

Probably Method 3 and 4 might have almost the same performance but just posting to confirm.

推荐答案

据此JSBen.ch测试，switch 设置是提供的方法中最快的(Firefox 8.0 和 Chromium 15).

According to this JSBen.ch test, the switch setup is the fastest out of the provided methods (Firefox 8.0 and Chromium 15).

方法 3 和 4 的速度稍慢，但几乎不明显.显然，if-elseif 方法的速度要慢得多(FireFox 8.0).

Methods 3 and 4 are slightly less fast, but it's hardly noticeable. Clearly, the if-elseif method is significantly slower (FireFox 8.0).

Chromium 15 中的相同测试未显示这些方法之间的性能存在显着差异.事实上，if-elseif 方法似乎是 Chrome 中最快的方法.

The same test in Chromium 15 does not show significant differences in performance between these methods. In fact, the if-elseif method seems to be the fastest method in Chrome.

我已经再次运行了测试用例，另外还有 10 个条目.hrefmap(方法 3 和 4)表现出更好的性能.

I have run the test cases again, with 10 additional entries. The hrefmap (methods 3 and 4) show a better performance.

如果你想在函数中实现 compare 方法，方法 3 肯定会胜出:将映射存储在一个变量中，然后在稍后引用这个变量，而不是重新构建它.

If you want to implement the compare method in a function, method 3 would definitely win: Store the map in a variable, and refer to this variable at a later point, instead of reconstructing it.

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