member function in javascript 'function'/object is saying it is not a function

Question

I am trying to review some basic Javascript using an online environment where print() is allowed. However, when I try to call say() on an instance of the person, it is saying that "say" is not a function. I have tried this in several different environments with their version of print (be it writeln, console.log, or whatever) and it's always saying it's not a function.

//JavaScript-C24.2.0 (SpiderMonkey)

print("Hello, world!")

function person(name, age) {
    this.name = name;
    this.age = age;
    this.say = function () {
        print(this.name);
    }
}

var arrayz = [];

arrayz.push(person("bob",20));
arrayz.push(person("sally",19));
arrayz.push(person("joe",22));

for (var z in arrayz) {
       z.say();
}

I'm doing it in just the same manner as this is: https://developer.mozilla.org/en-US/docs/Learn/JavaScript/Objects/Object-oriented_JS

So I don't see what I'm doing wrong. Can someone please help me with what I'm doing wrong here?

Answer 1

The correct code should be:

print("Hello, world!")

function person(name, age) {
    this.name = name;
    this.age = age;
    this.say = function () {
        print(this.name);
    }
}

var arrayz = [];

arrayz.push(new person("bob",20));
arrayz.push(new person("sally",19));
arrayz.push(new person("joe",22));

for (var z of arrayz) {
       z.say();
}

Let me explain. The first difference is the new keyword. This creates a new instance of the function you've made as an object. The way you did it just called person as a function. So it stores the returned value of person into the the array instead of the object instance. Since person doesn't return a value it stores undefined into your array.

More info about the new operator: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/new

Second, you used var z in arrayz . When using in , z becomes the index instead of the object. If you want the z to be the value of the array item you should use var z of arrayz

More info about for...in : https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for...in

More info about for...of : https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for...of

Answer 2

Solution :

Using new person(...) instead of person(...) will create the object you want, filled with properties you specified by writing this.xxx = yyy in the function body.

Explanation of your error :

You are simply calling the function, meaning that you are trying to get its the return value and push it in the array.

I don't see any return statement in your function person , so the result is undefined .

You have pushed 3 undefined in your array, and you try to execute say() on them.