如何用原型覆盖属性

Question

How to override a property with prototype in Javascript?

code

function Test(){
    this.prop = false;
}

Test.prototype.prop = true;

var T = new Test();
console.log(T.prop);

this returns false but should return true ??

Answer 1

If you need to change the value of the t property access the property directly from an instance of the object or specify it in the constructor.

Direct Access

var T = new Test();
t.prop = false;
console.log(T.prop);

Constructor

function Test(prop){
    this.prop = prop;
}

var T = new Test(false);

Answer 2

The constructor is executed after the prototype copy. You can't override a property setted by a constructor by using the prototype.

But if you really want to do this, you can do this :

function Test(){
    if (this.prop === undefined) {
        this.prop = false;
    }
}