JavaScript访问对象属性的运行时复杂度O(?)是多少? [英] What is the run time complexity O(?) for JavaScript to access an object property?

问题描述

var obj = {};

obj["A"] = true;
obj["B"] = true;
obj["C"] = true;

console.log(obj["D"]);

上面的代码将打印"undefined".当javascript试图访问obj ["D"]时，运行时复杂度是多少?我想它将与尝试访问obj ["A"]一样?

The above code will print "undefined". What is the runtime complexity when javascript is trying to access obj["D"] ? I guess it will be the same as it is trying to access obj["A"]?

之所以这样问，是因为我正在比较这两个代码之间的效率:

The reason why I am asking this is because I am comparing the efficiency between these two code:

//Code 1
var x = ["a","b","c"];
var y = ["a","b","c"];

for(i = 0; i<x.length; i++){
    for(j = 0; j<y.length; j++){
        console.log(i==j);
    }
}

//Code2
var _x = {};
var _y = ["a", "b", "c"];

_x["a"] = true;
_x["b"] = true;
_x["c"] = true;

for(i = 0; i<_y.length; i++){
    if(_x[_y[i]] != undefined){
        console.log("something");
    }
}

我想知道在运行时复杂度方面哪个效率更高.我想如果访问一个对象属性需要O(n)，那么两个代码的运行时间将是相同的吗?

I would like to know which one is more efficient in term of runtime complexity. I suppose if accessing an object property takes O(n), then the runtime of the two code would be the same?

推荐答案

JavaScript语言对操作的时间复杂度没有任何要求，因此性能将取决于您使用的JavaScript解释器.

The Javascript language doesn't set any requirements on the time complexity of operations, so performance will depend on the Javascript interpreter you're using.

(在某些情况下，它甚至可能不是固定的；大多数现代Javascript解释器会执行运行时优化，这可能会更改操作的时间复杂性.)

(In some cases, it may not even be fixed; most modern Javascript interpreters perform runtime optimizations which may change the time complexity of operations.)

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