javascript prototype method not defined

Question

Im trying to become more object orientated in my approach to doing things and ive run into an error where the console says a function is undefined. I cant see how because i have other functions that run that have the same makeup.

i set up my object like this in my app.js:

var vid = new videoAPI(whichOs.type());

Then i set up my constructor in my lib.js:

function videoAPI(osParam)
{
    this.os = osParam;
}

And create my methods the one I have issues with is this one in my lib.js:

videoAPI.prototype.print = function()
{
    return this.os;
}

I then call in my app.js

console.log(print());

I have two other functions that use this setup but i pass variables in. Can anyone tell me what im doing wrong?

**edit. The line it fails on is is print(); I didnt mention i have this in a node.js project linking two js files together. this is the error:

ReferenceError: print is not defined
    at Object.<anonymous> (C:\Users\denis\Desktop\videoServer\app.js:36:13)
    at Module._compile (module.js:460:26)
    at Object.Module._extensions..js (module.js:478:10)
    at Module.load (module.js:355:32)
    at Function.Module._load (module.js:310:12)
    at Function.Module.runMain (module.js:501:10)
    at startup (node.js:129:16)
    at node.js:814:3

Please show the actual line of code that triggers the error. — jfriend00
– jfriend00, Commented Jan 22, 2016 at 20:26
Copying your code into the console and then calling var vid = new videoAPI('A'); works with no errors. — nem035
– nem035, Commented Jan 22, 2016 at 20:27
Hmmm that works @Grundy but i have two other functions that dont need the prefix 'vid.' is there any reason why this needs it? — Dennington-bear
– Dennington-bear, Commented Jan 22, 2016 at 20:34
those two other functions probably exist globally off the window object. — Seth
– Seth, Commented Jan 22, 2016 at 20:34

michael · Accepted Answer · 2016-01-22 20:34:30Z

1

Based on the code provided, print is a prototype on the videoAPI object, but in the console log you're simply calling print. Change:

console.log(print());

To:

console.log(vid.print());

It should fix your problem.

EDIT: Looks like Seth beat me to it :P

answered Jan 22, 2016 at 20:34

michael

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Seth · Accepted Answer · 2016-01-22 22:35:19Z

1

You need to actually call the method off of the videoAPI instance.

var vid = new videoAPI('something');
console.log(vid.print()) // returns: something

If you're calling other functions without prefixing them with the videoAPI instance variable, then they exist globally.

edited Jan 22, 2016 at 22:35

answered Jan 22, 2016 at 20:34

Seth

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