Is there a javascript equivalent of python's getattr method?

Question

In python you can define a object having __getattr__(self,key) method to handle all unknown attributes to be solvable in programmatic manner, but in javascript you can only define getters and setters for pre-defined attributes. Is there a generic way of getting the former thing done also in javascript?

Sample code would be smth like:

function X() {};
X.prototype={
  __getattr__:function(attrname) {
    return "Value for attribute '"+attrname+"'";
  }
}

x=new X()
alert(x.lskdjoau); // produces message: "Value of attribute 'lskdjoau'"

Key point is getting value of attribute programmatically depending on the name of the attribute. Pre-setting attribute does not help because during init there is no information what attributes might be requested.

Adding this as comment as question is closed. For js newbies coming from a python background as I am, what I was looking for was, for `__getattr__`, `myObj[myKey]`, and for `__hasattr__`, `myObj.hasOwnProperty(myKey)`. — Théo Rubenach, May 19 '20 at 17:11

score 67 · Answer 1 · edited Apr 13 '20 at 09:25

67

It's now possible if your browser has support for the ES6 Proxy feature. You can check this in the ECMAScript 6 compatibility table.

If you have the proxy support, you would use it as follows:

let handler = {
  get(target, name) {
    return `Value for attribute ${name}`
  }
}

let x = new Proxy({}, handler);
console.log(x.lskdjoau); // produces message: "Value of attribute 'lskdjoau'"

Works in chrome, firefox, and node.js. Downsides: doesn't work in IE - freakin IE. Soon.

edited Apr 13 '20 at 09:25

user2226755

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answered May 13 '15 at 20:43

Jan Sabbe

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Holy crap I've been waiting for this!!! – B T Mar 20 '16 at 07:30
Looks like you packaged it. https://github.com/alexmojaki/sorcery#dict_of Nice work! – kzahel Jun 25 '19 at 03:11
Its still not clear to me. Any jsfiddle? – AhmedRana Jun 28 '19 at 15:28

score 11 · Accepted Answer · edited May 23 '17 at 12:32

11

Sadly the answer is No. See Python's __getattr__ in Javascript

You've got __defineGetter__, but as you noted you need to know the name of the attribute you will be accessing.

By the way I think you meant __getattr__ (__getitem__ is for things you want to access with []).

edited May 23 '17 at 12:32

Community

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answered Oct 07 '09 at 04:55

Roatin Marth

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thanks. yes, it would be rather __getattr__ – Oct 20 '09 at 07:32
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@Roatin WHY!!!! JS needs this more than any other feature (except the 'less suck' feature that people have been requesting for a decade). – orokusaki Feb 10 '10 at 21:07

Is there a javascript equivalent of python's getattr method?

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Is there a javascript equivalent of python's __getattr__ method?

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Is there a javascript equivalent of python's getattr method?