避免使用var可以减少内存使用吗？

Question

Let's say I have a class MyClass with a function method() that is going to be called a lot . Which of these implementations is going to be more efficient?

function MyClass() {
    this.method = function () {
        var number = 10;
        var boolean = true;
        var string = "string";

        // do something
    };
}

function MyClass() {
    this.data = {};
    this.method = function () {
        this.data.number = 10;
        this.data.boolean = true;
        this.data.string = "string";

        // do something
    };
}

The first implementation creates new variables which will be eligible for garbage collection after the execution of the function since there's no reference to them, which is great. However, if I call the function 3 times, there is memory allocated for a total of 3 numbers, 3 booleans and 3 strings.

The second implementation doesn't create new variables, it simply overwrites the values of the previous call of the function instead. Does this mean that after 3 invocations of the function, the memory allocated is just for 1 number, boolean and string, instead of 3? Is there really 3 times less memory consumed?

Answer 1

function MyClass() {
    this.method = function () {
        var number = 10;
        var boolean = true;
        var string = "string";

        // do something
    };
}

First approach is better as the variables are method scope and will be collected by GC once method execution is complete. But keep in mind if you have to keep these values as class members then this method will not work.

In second approach you are attaching these properties with class reference. So GC will not collect it until the class instance is referenced with some scope.

Answer 2

Your second approach looks very logical and accessible. I believe code is poetic and it tells a lot about persistence.

function MyClass() {
    this.data = {};
    this.method = function () {
        this.data.number = 10;
        this.data.boolean = true;
        this.data.string = "string";

        // do something
    };
}

the above code looks efficient and well structured than creating more var every single time your class is called.