Calling a function on assignment in JavaScript

Question

I'm pretty sure this is impossible but maybe someone clever out there knows if there is a chance of making this work. Is it possible to have code where:

1    myPerson = new Person();
2    myPerson.name = 'Charles Xavier';

Where the code on line #2 automatically checks if myPerson.setName exists and if so calls

myPerson.setName('Charles Xavier');

in place of of doing the direct assignment.

Create a helper function which does the check for you? Or why dont you do the check inside setName()? — stackErr
– stackErr, Commented Apr 17, 2014 at 15:12

Aegis · Accepted Answer · 2014-04-17 15:14:46Z

2

Nope, sorry! It is possible in ES6, though:

var o = {};
Object.defineProperty(o, "name", {
  set: function (value) {
    console.log("Property 'name' set to: " + value);
    // store 'value' somewhere
  }
});

c.f. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperty

related: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/create

Since this is not possible in < ES6, frameworks like AngularJS use dirty-checking (aka they check the value X times per second) to watch for property changes.

answered Apr 17, 2014 at 15:14

Aegis

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2 Comments

Kirk Ouimet Over a year ago

Dirty checking sounds terrible! Very cool that this type of functionality is coming with ES6 though.

Aegis Over a year ago

@Kirk haha it does sound terrible but it works pretty well for AngularJS.

Iqbal Fauzi · Accepted Answer · 2014-04-17 15:18:41Z

1

Not for all browser, but there's javascript proxy which is only work on firefox, and make this become useless. :D

var Validator = {
    set: function(obj, prop, value){
        if(prop == 'name' && setName in obj)
            obj.setName(value);

        obj[prop] = value;
    }
}

var myPerson = new Proxy(Person, Validator);
myPerson.name = 'Charles Xavier'; // This will call Validator.set

answered Apr 17, 2014 at 15:18

Iqbal Fauzi

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