Is it possible to use a constructor in a Javascript object literal to avoid instantiation?

Question

I have an object that needs certain properties to be set by execution instead of assignment. Is it possible to do this using a literal object notation?

I would like to be able to access the object's properties using this:

myObject.propertyName

...rather than this:

objInstance = new myObject();
objInstance.propertyName;

EDIT: to clarify, based on Bergi's answer, this is what I'm aiming to do:

var myObj = {
    myInfo: (function() { return myObj.getInfo('myInfo'); })(),
    getInfo: function() { 
      /* lots of execution here that would be redundant if done within myInfo */
    }
}

// access the calculated property value
myObj.myInfo;

But this gives me the error myObj is not defined

If you don't get useful answers it might be that I'm not the only one who didn't understand your question. In that case a little more code might be a valuable addition. — Denys Séguret, Feb 25 '14 at 18:07
@Bergi: sorry, I thought this was less obscure term than it actually is :) http://dictionary.sensagent.com/instantialization/en-en/ — Recovering Nerdaholic, Feb 25 '14 at 18:13
@Recovering: Ah, since there are neither templates nor static typing in JS I've never heard of it (and it doesn't really apply). I've first thought of a portmanteau from *instantiation* (creating an object) and *initialisation* (executing the constructor) — Bergi, Feb 25 '14 at 18:28
"instantiation" ... that's the word I was looking for. I guess it overcomplexitized it :) — Recovering Nerdaholic, Feb 25 '14 at 18:37
no, literals can only create native constructor instances. you can use Object.defineProperty to do anything you want upon execution. — dandavis, Feb 25 '14 at 18:40

score 2 · Answer 1 · edited May 23 '17 at 10:31

2

I guess what you want is an IEFE, which you can put inside an object literal:

var myObject = {
    propertyName: (function() {
        var it = 5*3; // compute something and
        return it;
    }()),
    anotherFunction: function() {…}
};

myObject.propertyName // 15

Maybe you also want to use the module pattern. Have a look at Simplest/Cleanest way to implement singleton in JavaScript?.

edited May 23 '17 at 10:31

Community

1
1

answered Feb 25 '14 at 18:10

Bergi

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This is very close to what I need, but how do I call another function defined as a property of the object? It results in an error `[object] is not defined` – Recovering Nerdaholic Feb 25 '14 at 18:35
No idea what your code looks like. But you just would put the functions on the object literal as usually. – Bergi Feb 25 '14 at 18:41
1

@RecoveringNerdaholic: Or do you mean calling them from the IEFE? That won't work, as the object doesn't yet exist when it is executed. Use the module pattern then. Also check out https://stackoverflow.com/questions/4616202/self-references-in-object-literal-declarations – Bergi Feb 25 '14 at 18:43
@Bergi: That's it! The module pattern. Thanks! – Recovering Nerdaholic Feb 25 '14 at 18:59

score 0 · Accepted Answer · answered Feb 25 '14 at 19:05

Thanks to Bergi to finding this, here is a final example what I wanted to do:

myObj = {
   init: function() {
        this.oneProperty = anyCodeIWant...
        this.anotherProperty = moreCodeIWant...
        // and so on
        return this;
   }
}.init();

myObj.oneProperty;
myObj.anotherProperty;
// and so on

Is it possible to use a constructor in a Javascript object literal to avoid instantiation?

2 Answers2