How do you properly clear Aurelia binding of a complex object? - aurelia

Question

Background: I'm trying to create a form using Aurelia. I have a person object that I would like to be able to fill in data for. If the user knows some identifying information about the person's family, they can enter it in an input and a select box will be displayed to allow the user to select the individual from that family for this particular form. The form will then fill in any information it knows about that individual into input fields allowing the user to overwrite any of the information if necessary. The form also allows them to clear the selected person if they want to choose another one.
Most of the functionality seems to work as expected, but when I try to allow the user to clear out the selected person, I'm seeing some behavior that I wouldn't have expected.
I have created a GistRun. The bottom pane is working as I would expect, after the user gets data, selects a person and then clears their selection, they are provided with the select element again. If you uncomment the input element, you will see that the user now has to click the clear action twice before they see the select element again. Why?
How can I update the application so that the user will only need to clear out the person once and the select box will appear again to allow the user to make another selection?
If you have an Aurelia application, you should be able to reproduce this by replacing the app.html with the following:
<template>
<select value.bind="val2" if.bind="opts2 && !val2">
<option repeat.for="opt of opts2" model.bind="opt">${opt.firstName}</option>
</select>
<div if.bind="!opts2 || val2">
<span>${val2.firstName}</span>
<button click.delegate="clearVal2()" if.bind="val2">Clear</button>
</div>
<button click.delegate="getOpts2()">Get</button>
<div>${val2.blah}</div>
<!--<input type="text" value.bind="val2.blah"/>-->
</template>
An the app.js with this:
export class App {
opts2;
val2;
getOpts2(){
this.opts2 = [
undefined,
{
blah: 1,
firstName: 'foo',
address: {
line1: '123 Main St.'
}
},
{
blah: 2,
firstName: 'bar',
address: {
line1: '456 Other Wy.'
}
}
];
}
clearVal2(){
this.val2 = null;
}
}
Any help would be greatly appreciated. Thanks!
UPDATE
If I put the input in a custom element and bind to that, things seem to work as expected. The values that I'm putting into my form though aren't in one location that I could utilize a custom element for. I have updated the Gist with an example.
How can I achieve the same functionality without the need for a custom element?

Answer 1

In all honesty I'm not sure why, but if you add if.bind="val2"on the input element, it clears the value and the select button returns.
<input type="text" if.bind="val2" value.bind="val2.blah"/>
Hope this (slightly) helps

Answer 2

Give that you are allowing the user to either select a value from the list or create a completely new entry, I would tend towards separating the value selected in the list and the data backing up the text boxes. Whenever the value of the select changes, I would set the value of the object backing the text boxes to the value of the select. The way I chose to do this in my sample code is to use the observable decorator on the value the select is bound to.
Here's an example: https://gist.run?id=e4b594eaa452b47d9b3984e7f9b04109
app.html
<template>
<div>
<select value.bind="val" if.bind="opts && !val">
<option repeat.for="opt of opts" model.bind="opt">${opt.firstName}</option>
</select>
<button click.delegate="getOpts()">Get</button>
</div>
<div if.bind="!opts || person">
<span>First Name: ${person.firstName}</span>
<button click.delegate="resetForm()" if.bind="val">Clear Selection</button>
</div>
Address: <input type="text" value.bind="person.address.line1" />
<hr />
val
<pre><code>
${toJSON(val)}
</code></pre>
person
<pre><code>
${toJSON(person)}
</code></pre>
</template>
app.js
import {observable} from 'aurelia-framework';
export class App {
#observable val = null;
person = {};
getOpts(){
this.opts = [
null,
{
blah: 1,
firstName: 'foo',
address: {
line1: '123 Main St.'
}
},
{
blah: 2,
firstName: 'bar',
address: {
line1: '456 Other Wy.'
}
}
];
}
valChanged() {
this.person = this.val;
console.log("set person");
}
resetForm(){
this.val = null;
console.log("reset val");
}
toJSON(value) {
if(!(value === false) && !value) {
return '';
}
return JSON.stringify(value);
}
}
You can see something interesting is happening when I reset the form. Aurelia is creating the properties necessary for bindings to person (namely person.address.line1 when we set person = null. But it doesn't create a firstName property, b/c that property isn't being bound until person stops being falsey.

Answer 3

Another option here is to simply use the with attribute to scope the input.
https://gist.run/?id=7b9d230f7d3c6dc8c13cefdd7be50c7f
<template>
<template with.bind="val.address">
<input value.bind="line1" />
</template>
</template>
Although I agree that mixing the logic of selections and inputs like that is probably not the best idea :)