Does afterRender work with Knockout components?

Question

afterRender works with template bindings, but after converting my templates to components, there does not seem to be any way to use afterRender. I have tried looking for an example of a component that uses afterRender, but cannot find anything.

Answer 1

I could not get the method working as per the above post. However i found a workaround on the git issue list and it doesn't require a custom KO Binding.

Add the below line in your component template html or string of code.

 <span data-bind="template: { afterRender: init }"></span>

Then create a init function in your module / viewModel:

 this.init = function() {
   Do cool DOM stuff here.
}

or depending on your viewModel structure:

viewModel: function(params) {
    return {
        init: function () {

        }
    };
},

Works like a charm. Example of it working is here

http://jsfiddle.net/gLcfxkv6/1/

Thread on knockout git here: https://github.com/knockout/knockout/issues/1533

Thanks to vamps on git for the workaround.

Answer 2

The secret here is http://knockoutjs.com/documentation/custom-bindings.html

ko.bindingHandlers.myCustomBinding = {
  init: function(element, valueAccessor, allBindings, viewModel, bindingContext) {
    // This will be called when the binding is first applied to an element
    // Set up any initial state, event handlers, etc. here
    if (bindingContext.$data.init) bindingContext.$data.init(element, valueAccessor, allBindings, viewModel, bindingContext);
  },
  update: function(element, valueAccessor, allBindings, viewModel, bindingContext) {
    // This will be called once when the binding is first applied to an element,
    // and again whenever any observables/computeds that are accessed change
    // Update the DOM element based on the supplied values here.
    if (bindingContext.$data.update) bindingContext.$data.update(element, valueAccessor, allBindings, viewModel, bindingContext);
  }
};

so in my component template I do something like

<div class="row-fluid" data-bind="myCustomBinding: 'someValue'">

and on the component viewModel I just implement init and/or update, for example:

constructor.prototype.init = function(element, valueAccessor, allBindings, viewModel, bindingContext) {
  // All the buttons in the buttons group need the same name,
  // but they all need distinct ids. We use timestamps because
  // as components, the names and ids should be distinct across
  // multiple instances of each component.
  var timeStamp = new Date().getTime();
  $('input:radio').attr('name', timeStamp).button();
  $('input:radio:eq(0)').attr('id', timeStamp+1);
  $('input:radio:eq(1)').attr('id', timeStamp+2);
  $('input:radio:eq(2)').attr('id', timeStamp+3);

  // Initialize the number-picker
  $('input[name="number-picker"]').TouchSpin();
};

The Knockout documentation could be improved by pointing out this very useful case. Also, this is such a useful binding, there should be a standard bindings for 'init' and 'update', for example

<div data-bind="init: 'someValue'">

Answer 3

We needed to access DOM elements in a component after switching between different components. We would have liked to use the non-existing "afterRender" binding on components.

We solved it with a Javascript setTimeout, letting KO do its rendering first, and in effect queueing our code after that.

HTML:

<div data-bind="component: compName"></div>

The code switching the component:

var compName = ko.observable();

//...

compName(switchToComponent);
setTimeout(function(){
    // this code is queued until after the component is rendered.
}, 0);

Answer 4

As of knockout 3.5.1, you can add a koDescendantsComplete function to your viewModeland that will be triggered after the rendering is complete

var viewModel = {
    koDescendantsComplete: element => {
        console.log( 'Rendered!', element );
    }
}

See: https://github.com/knockout/knockout/blob/2db9f7f79939ed289621de72340ab048362ed76b/src/components/componentBinding.js#L73

Answer 5

Make a new binding, like so

ko.bindingHandlers.initBinding = {
init: function (element, valueAccessor, allBindings, viewModel, bindingContext) {
    debugger
    if (valueAccessor() && valueAccessor().afterRender && bindingContext.$data) {
        valueAccessor().afterRender(bindingContext.$data);
    }
},
update: function (element, valueAccessor, allBindings, viewModel, bindingContext) {
    }
};

export default ko.bindingHandlers.initBinding

You don't need the export if you're not using ES6(babel etc).

Then in your component html, you can do something like this

<div class="staff-directory" data-bind="initBinding: {afterRender: afterRender }">
    <p>Loaded</p>
</div>

And in your component model

class staffDirectory {

    constructor() {
        console.log('staff directory loaded');
    }

    afterRender() {
        console.log('afterRender called');
    }

}

export default staffDirectory;