Aurelia disable button on validation errors

disabledIfNotValid.ts

import {customAttribute, inject} from 'aurelia-framework'
import {ValidationController} from 'aurelia-validation'
import * as jQuery from "jquery";

@inject(Element)
@customAttribute('disabled-if-not-valid')
export class DisabledIfNotValid {
    private element: JQuery;
    private controller: ValidationController;

    constructor(element: Element) {
        this.element = jQuery(element);
        this.element.prop('disabled', true);
    }

    valueChanged() {
        let errorCount = this.controller.errors.length;
        if (errorCount === 0) {
            this.controller.validate();
        }
        this.element.prop('disabled', errorCount !== 0);
    }

    bind(bindingContext:{controller:ValidationController}) {
        this.controller = bindingContext.controller;
    }
}

view.html

<button class="btn btn-space btn-primary" disabled-if-not-valid="${controller.errors}" click.delegate="save()">Save</button>
                                    

This looks like a good reusable solution. However, I think I would have used disabled-if-not-valid.bind="controller.errors" instead of disabled-if-not-valid="${controller.errors}".