About Object methods in Javascript

Question

I'm trying to create a class method but I don't see what I am doing wrong here. Here is my code

var Invoice = function(title) {
this.title = title;

this.addItem = function addItem(item_name) {
  console.log("Hello, you added " + item_name);
};

invoice = new Invoice("Video games")
invoice.addItem('Xbox 360');

I get the following error:

TypeError at line undefined: invoice.addItem is not a function

@Mahi: That doesn't actually matter. It's valid to give a function expression a name. — , Nov 30 '16 at 18:56
Jamie: You posted an invalid code snippet because you're missing a `}` somewhere, so it won't run at all. If the closing `}` is *before* the `this.addItem = function...`, then that's your issue. — , Nov 30 '16 at 18:56
It is working. Could you copy & paste the code in console and run(after closing bracket in the function )? — maheshiv, Nov 30 '16 at 18:59
Try Invoice.prototype.addItem = function(item_name){here your code} and add missed }. — rad11, Nov 30 '16 at 18:59

score 3 · Accepted Answer · edited May 23 '17 at 12:30

3

Simple typo, which goes to show why proper indentation is ESSENTIAL:

var Invoice = function(title) {
    this.title = title;
    this.addItem = function addItem(item_name) {
         console.log("Hello, you added " + item_name);
    };
};  //you were not closing your constructor

You could, and probably should use prototype.

var Invoice = function(title) {
    this.title = title;
};
Invoice.prototype.addItem = function(item_name){
     console.log("Hello, you added " + item_name);
};

For a detailed explanation of the difference, see JS - why use prototype

or in ES6, with a class :

class Invoice {
     constructor(title){
         this.title = title;
     }
     addItem(item_name) {
          console.log("Hello, you added " + item_name);
     }
}

And in case your invoice is a node module, and your question is made of concatenated code, don't forget to add :

module.exports = Invoice;

So you can require it anywhere.

In all those cases, invocation is done in the same way :

let invoice = new Invoice("Video games") //or var if ES5
invoice.addItem('Xbox 360');

edited May 23 '17 at 12:30

Community

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answered Nov 30 '16 at 18:59

xShirase

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The typo is most likely just in the question, otherwise it would be a SyntaxError instead of a TypeError. – Nov 30 '16 at 19:00
`TypeError at line undefined:` seems suspicious – xShirase Nov 30 '16 at 19:01
Yes, I wonder if that's output from running in a console. In any case, that placement of `}` does fix it, though I'd imagine the OP would want the function on the `Invoice.prototype`. – Nov 30 '16 at 19:03
:p been there, done that – xShirase Nov 30 '16 at 19:05
So, using ES6. How do I make it return `[Invoice "Video games"]` when the new instance is created? – Jaime Rios Nov 30 '16 at 19:27
@JaimeRios see edit – xShirase Nov 30 '16 at 19:37

About Object methods in Javascript

1 Answers1