automatically create object structure

[devmondo]

hi, i have the following scenario where i have user object

let user ={}

when i bind in html like this

<input value.bind="user.personal.name">

i get undefined in the textbox, but if i make user like this let user={personal:{}}
undefined in textbox goes away, i can understand this behavior if we are using something like c# because it is a statically typed languge but javascript is dynamic and left this constrain from us.

please consider this, thanks in advanced.

[jdanyow]

gitter discussion: ☝️ July 7, 2015 4:46 PM

The request is to make the binding system automatically "define" undefined path expressions.

Binding behavior maybe?

[EisenbergEffect]

@devmondo Do you mean that you get the word "undefined" appearing in the text box? If so, I think we should look into fixing that in the core.

[devmondo]

@EisenbergEffect yeah exactly, it is really troublesome with huge object structure, thanks :)

[jdanyow]

@devmondo are you still able to reproduce this? This example works for me using the current bits:

export class App {
  user = {};

  constructor() {
    setInterval(() => this.debug = JSON.stringify(this.user), 500);
  }
}

<template>
  <p>user = ${debug}</p>

  <input type="text" value.bind="user.personal.name">
</template>

[devmondo]

@jdanyow it is working :) so you guys worked on it to make sure it is not false alarm?

[jdanyow]

Nice- yeah I was just going through the binding repo issues to see what was outstanding.

[devmondo]

i dont know if it is me or not, but if i do this

 this.user.personal.numbers=[1,2,3];

i get inner error: TypeError: Cannot set property 'cool' of undefined
unless i do this

 this.user.personal={};

[EisenbergEffect]

My guess is that your "personal" reference is undefined. We don't actually change your objects (I don't think), but the binding system can safely evaluate undefined paths. For your own code in JS, you will need to handle setting up all the references.

[jdanyow]

@EisenbergEffect / @devmondo here's a plunkr that shows what happens:

http://plnkr.co/edit/HnNmfzVqnQhsOkQCWpXn?p=preview

once you type in the textbox you'll see the feature that @devmondo was asking for (magic creation of object structure). Personally I think this is weird and would not expect it to work this way but hey- it works 😉

Here's the code I think is responsible: https://github.com/aurelia/binding/blob/master/src/ast.js#L240-L243

[EisenbergEffect]

Ah yes....it does work. I remember that.

[devmondo]

@jdanyow @EisenbergEffect i know it is weird, but sometimes it is really needed :) but hey you guys know what can and cant be done