类定义的首选JavaScript惯用法

Question

What is the preferred idiom for defining a class in JavaScript? I could define a constructor function for complex numbers as follows:

function Complex(real, imag) {
    this.real = real;
    this.imag = imag || 0.0;
    this.add = function(other) {
        this.real += other.real;
        this.imag += other.imag;
        return this;
    }
}

or I could do the following:

function Complex(real, imag) {
    this.real = real;
    this.imag = imag || 0.0;
}

Complex.prototype = {
    add : function(other) {
        this.real += other.real;
        this.imag += other.imag;
        return this;
    }
}

Since neither textbook JavaScript : The Good Parts nor JavaScript The Definitive Guide define classes the first way I suspect these are not equivalent -- I suspect I need use prototype if I plan on using inheritance. This seems a little murky to me -- can anyone clarify this?

I know I could use the Object.create() method suggested in the aforementioned texts and do things the prototypical way, but I don't see folks doing this in practice much.

Answer 1

In the first example, every new object get's its own copy of the add() method.

In the second example, every new object share's a single copy of the add() function via the prototype .

Obviously the latter is more efficient.