Javascript寄生构造函数似乎无法向对象添加函数，为什么

Question

I get this example from internet, using parasitic constructor to build an object, including giving it an extra function:

function SpecialArray(){
    var values=new Array();
    values.push.apply(values, arguments);
    values.toPipedString=function(){
        return this.join("|");
    }
}

var colors=new SpecialArray("red", "blue", "green");
console.log(colors.toPipedString());

Well the code runs with an exception:

console.log(colors.toPipedString());
                   ^
TypeError: colors.toPipedString is not a function

But I think I've attached the function to the object. Why it says function is not there?

Thanks.

Answer 1

You attaching toPipedString function to internal var. Try this:

function SpecialArray() {
    var values=new Array();
    values.push.apply(values, arguments);
    this.toPipedString = function() {
        return values.join("|");
    }
}

var colors = new SpecialArray("red", "blue", "green");
console.log(colors.toPipedString());

Answer 2

If you wanted to call toPipedArray as a function of specialArray, it needs to be on the prototype of special array.

function SpecialArray(){
    this.values=new Array();
    this.values.push.apply(this.values, arguments);

}
SpecialArray.prototype.toPipedString = function(){
    return this.values.join("|");
}
var colors=new SpecialArray("red", "blue", "green");
console.log(colors.toPipedString());

Nosyara's approach works as well. Using this.Myfunction within the function/object puts myFunction on the prototype as well.