Aurelia custom attribute to invoke a callback when an element gets added to the dom. Demo: http://plnkr.co/edit/fguuz4

attached.js

import {customAttribute, bindable, LogManager} from 'aurelia-framework';

const logger:Logger = LogManager.getLogger("attached");

/**
 * MIT License. Patrick Eisenmann.
 * Apply this attribute to an element to have a callback invoked when the element added to the DOM
 *
 * @param {Function} callback. Required. The function to be invoked.
 *                             The first argument to the callback is the Element that had the attached on it.
 *                             Any arguments specified by the args parameter will be passed as individual args after the element.
 * @param {Object|ViewModel} scope. Optional. The thisArg of the callback when invoked.
 * @param {Array} args. Optional. Additional arguments passed to the callback.
 *
 * Example:
 *
 * foo-view.js

 export class FooView {
   constructor() {
     this.$this = this;
     this.elements = {};
     this.data = [{
       id: 10000,
       name: 'Hello'
     },{
       id: 10001,
       name: 'World'
     },{
       id: 10002,
       name: 'Tomato'
     }];
   }

   mySubElementAttached(element, index) {
     $(element).someJQueryPlugin();
     this.elements[index] = element;
   }
 }

 * foo-view.html
 <template>
   <require from="attributes/attached"></require>
   <div repeat.for="datum of data" attached="callback.bind: $parent.mySubElementAttached; scope.bind: $parent.$this; args.bind: [$index]">
       ${$index}: ${datum.id}: ${datum.name}
   </div>
 </template>

 */

@customAttribute('attached')
export class Attached {

  @bindable callback;
  @bindable scope;
  @bindable args;

  static inject = [Element];
  constructor(element) {
    this.element = element;
  }

  attached() {
    logger.info("Attached!", this.args);
    if (typeof this.callback === 'function') {
      this.callback.apply(this.scope, [this.element, ...(this.args || [])]);
    }
    else {
      logger.error('Callback was type', typeof this.callback, ', not a function. Did you forget to callback.bind? Callback: ', this.callback, ' Scope: ', this.scope, 'Args: ', this.args);
      throw `attached attribute invoked, but callback was '${this.callback}' instead of a function.`;
    }
  }
}

I used this to achieve what I wanted in my own attribute, thank you for this code. The way you handled the scope was not ideal for me and after a lot of struggling I found a way around it. If you have the following code:
bind(bindingContext) { this.bindingContext = bindingContext; }
then you can replace this.callback.apply(this.scope, [this.element, ...(this.args || [])]); with this.callback.apply(this.bindingContext, [this.element, ...(this.args || [])]); and you would not have to rely on scope.bind: $parent.$this; in the view.

I have not tested it on your code but I presume it will work since it worked on mine that was copied from yours.

A new context is created when repeat.for is used. bindingContext will contain the child context and not the parent context. Under such conditions, you need to pass scope.