Mastering ngTemplate

ngBackbone advantages from NgTemplate - a light-weight DOM-based template engine, inspired by AngularJS. When we bind data (models/collections) to a component, any change on them triggers the template to re-synchronize. NgTemplate does it gracefully. It looks up the compiled template for the directives, evaluate the expressions and updates the directives only when expression has a changed state. For example in the component below we use data-ng-text directive to render world.name actual value into i element text node:

@Component({
  el: "ng-hello",
  models: {
    world: new Model({ name:  "Earth" })
  },
  template: `<i data-ng-text="world.name"></i>`
})

If the value changes this.models.get( "world" ).set( "name", "New world" ) the content of i element responds.

Template expressions

Template expressions are a JavaScript code that NgTempplate evaluates in the data scope (models/collections). So we can simply address a variable <i data-ng-text="world.name"></i> or run an expression <i data-ng-if="world.counter > 10"></i>

Expressions evaluate in the context of the target element, so we can access the element with this:

data-ng-if="foo && this.checked"

NOTE: In order to gain better performance keep to primitive expressions especially in cyclic directives e.g. data-ng-text="foo.bar.baz", data-ng-text="!foo.bar.baz", data-ng-text="'string here'", data-ng-if="foo.bar > baz.quiz", data-ng-text="foo + 10, data-ng-if="true", data-ng-prop="'disabled', true || false", data-ng-data="foo || bar, baz". Such expressions are being evaluated without use of eval() and therefore the process takes much less time and resources. You can check how the parser treats your expressions by studying content of template.report().tokens array

Directives

We use HTML-compliant data-ng-* custom attributes to tell the template how exactly we want to bind the scope data to the element

NOTE: data-ng-class, data-ng-prop, data-ng-attr, data-ng-data can be applied multiple times on an element like data-ng-class-0, data-ng-class-9

NgText

We use NgText to modify element's textNode

<i data-ng-text="foo"></i>

NgProp

We use NgProp to modify element's properties

<button data-ng-prop="'disabled', isDisabled"></button>

NgAttr

We use NgAttr to modify element's attributes

<input data-ng-prop="'required', isRequired">

NgData

We use NgData to modify element's dataset

<div data-ng-data="'dateOfBirth', value"></div>

NgClass

We use NgClass to modify element's classList

<i data-ng-class="'is-hidden', isHidden"></i>

NgIf

We use NgFor to toggle visibility of an element (subtree) within the DOM

<i data-ng-if="toggle">Hello!</i>

NgFor

We use NgFor when we need to generate a list of elements (subtrees)

<i data-ng-for="let row of rows" data-ng-text="row"></i>

NgSwitch

We use NgSwitch when we need to display on element (subtree) of a set of available options.

<div data-ng-switch="theCase">
    <i data-ng-switch-case="1">FOO</i>
    <i data-ng-switch-case="2">BAR</i>
    <i data-ng-switch-case-default>BAZ</i>
  </div>

NgEl

We use NgEl to modify element properties

NOTE: Using NgEl is rather discouraging as it cannot be cached and every model sync will cause the DOM modification even if the expression of NgEl wasn't changed

<i data-ng-el="this.textNode = mymodel.foo"></i>
<i data-ng-el="this.setAttribute( 'name', mymodel.foo )"></i>
<i data-ng-el="this.disabled = state.isVisible"></i>
<i data-ng-el="this.classList.toggle('name', model.foo)"></i>