Closed azl397985856 closed 4 years ago
贴个benchmark: node 版本: v10.20.1 机器: 2.6 GHz 六核Intel Core i7 16G
Switch | Object | |
---|---|---|
10 ^ 0 | 0.237ms | 0.083ms |
10 ^ 1 | 0.248ms | 0.108ms |
10 ^ 2 | 0.265ms | 0.259ms |
10 ^ 3 | 0.364ms | 2.264ms |
10 ^ 4 | 1.954ms | 13.573ms |
10 ^ 5 | 5.695ms | 63.255ms |
10 ^ 6 | 26.847ms | 546.769ms |
10 ^ 7 | 163.984ms | 5161.224ms |
10 ^ 8 | 1627.382ms | 50421.401ms |
let count = Math.pow(10, 8)
let swicthCount = count
let objectCount = count
const LOGIN_SUCCESS = "LOGIN_SUCCESS";
const LOGIN_FAILED = "LOGIN_FAILED";
const authState = {
token: "",
error: "",
};
function authReducer(state = authState, action) {
switch (action.type) {
case LOGIN_SUCCESS:
return { ...state, token: action.payload };
case LOGIN_FAILED:
return { ...state, error: action.payload };
default:
return state;
}
}
function authReducerObject(state = authState, action) {
const mapping = {
[LOGIN_SUCCESS]: { ...state, token: action.payload },
[LOGIN_FAILED]: { ...state, error: action.payload }
};
return mapping[action.type] || state;
}
console.time('switch')
while(swicthCount--) {
const action = Math.random() < 0.5 ? LOGIN_SUCCESS : LOGIN_FAILED
authReducer(authState, action)
}
console.timeEnd('switch')
console.time('object')
while(objectCount--) {
const action = Math.random() < 0.5 ? LOGIN_SUCCESS : LOGIN_FAILED
authReducerObject(authState, action)
}
console.timeEnd('object')
某些浏览器应该对switch做过优化,但是我觉得switch随着case数越来越多,性能肯定会下来,最终应该还是不如mapping,还有一个每次都是创建mapping对象,如果这个对象只初始化一次,也会有所提高
简单来说, if else 会自顶向下计算,时间复杂度最坏的情况是 $O(N)$。 而 switch case 使用类似 hash 的方式, 就条件和对应语句汇编到底层代码中,当程序执行的时候可以根据数学运算在 $O(1)$ 的时间定位到对应的代码块。
当然这并不是绝对的, switch 的优化方式可以参考这篇文章:https://www.cnblogs.com/182-7167-2685/p/5374111.html
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如下代码,是使用了switch case 的redux 的部分代码:
我们将核心代码改成mapping:
实现效果是一样的, 而且代码更简单明了。 通过benchmark测试,我们发现性能switch好很多,这是为什么?
附benchmark图: