> For the complete documentation index, see [llms.txt](https://dsheiko.gitbook.io/ng-backbone/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://dsheiko.gitbook.io/ng-backbone/template_syntax.md).

# Mastering ngTemplate

ngBackbone advantages from [NgTemplate](https://github.com/dsheiko/ng-template) - 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:

```javascript
@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`

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

### NgProp

We use `NgProp` to modify element's properties

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

### NgAttr

We use `NgAttr` to modify element's attributes

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

### NgData

We use `NgData` to modify element's dataset

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

### NgClass

We use `NgClass` to modify element's `classList`

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

### NgIf

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

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

### NgFor

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

```markup
<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.

```markup
<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

```markup
<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>
```


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