原型：Apply vs call，new vs create

Question

I have a constructor function which I want to use as prototype for another constructor. both receive arguments:

function Proto(arg) {}

function Sub(arg) {}

What's a better way to pass the argument from Sub constructor to Proto constructor:

Proto.apply(this, arg);

Proto.call(this, arg); (pun unintended...)

Second, when I want to actually set the prototype, what is the difference between:

Sub.prototype = Object.create( Proto );

Sub.prototype = new Proto();

Answer 1

The difference between .call and .apply is that .call takes its arguments as separate arguments for the function, while .apply takes the arguments as a single array. For example:

function myFunction(x, y) {
    var z;
    // Do something
    return z;
}

var context = {};

// The following function calls are equivalent:
var fx = myFunction.call(context, 5, 'h');
var fy = myFunction.apply(context, [5, 'h']);

In cases where you don't know the length of the argument list at compile time, you have to use .apply . But in this case you don't need to do that, and you can use the slightly simpler syntax of .call . If you were to do it with .apply , it would be Proto.apply(this, [arg]); .

As for Object.create versus new : Again, you've got the expression wrong, it should be Sub.prototype = Object.create(Proto.prototype); . I don't normally use Object.create , but as far as I can tell the only difference is the value of Sub.prototype.constructor . It probably doesn't matter much either way. However, the new way is more common and accepts arguments. (You can also give another argument to Object.create , but it works differently.)