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jQuery entwine

The following documentation regarding jQuery and Entwine does not apply to React components or sections powered by React. If you're developing new functionality in React powered sections please refer to React and Redux.

jQuery Entwine was originally written by Hamish Friedlander.

Entwine tries to provide a new model of code organisation - a replacement for Object Oriented programming that is focused on adding functions to groups of DOM elements based on the structure and contents of those DOM elements. It's a merging of the model and view layer that initially seems weird, but can give very powerful results.

Basics

Entwine applies methods, custom properties, and event handlers to elements in the DOM based on jQuery selectors. To attach entwine logic to DOM nodes, call the entwine function on a jQuery selector object and pass in an object which details any properties, methods, or event handlers which should apply to DOM nodes which match the selector.

$('div').entwine({
  // properties, methods, and event handlers go here
});

The definitions you provide are not bound to the elements that match at definition time. You can declare behaviour prior to the DOM existing in any form (i.e. prior to DOMReady) and later calls and event handlers will function correctly.

Selector specifity and "inheritance"

When there are two definitions for an event handler, method, or property on a particular DOM node, only the function with the most specific selector is used.

Specifity is calculated as defined by the CSS 2/3 spec. This can be seen as subclassing applied to behaviour. This is determined by the selector used for defining the entwine logic, not the selector used to select the DOM element.

For example, given this DOM structure

<body>
  <div>Internal text</div>
  <div class="attribute_text" rel="Attribute text"></div>
  <div>Nonsense</div>
</body>

And this entwine definition

$('div').entwine({
  foo() {
    // eslint-disable-next-line no-console
    console.log(this.text());
  },
});

$('.attribute_text').entwine({
  foo() {
    // eslint-disable-next-line no-console
    console.log(this.attr('rel'));
  },
});

Then this call, which only matches (and therefore only calls) the method for the element with the attribute_text CSS class

$('.attribute_text').foo();

Will log this to the console

Attribute text

And this call, which matches each of the div elements individually

$('div').foo();

Will log this to the console

Internal text
Attribute text
Nonsense

For selectors with the same level of specificity, the definition which is declared first takes precedence.

Calling less-specific logic from a definition with higher-specificity

There may be times when you want to apply additional logic to a method or event handler for a given DOM element, but still call the logic for the lower-specificity declaration. For example you might want to perform some conditional check before allowing a button click event to occur.

You can call the logic for the declaration with lower-specificity by calling this._super(). This special function can take any arguments, and will pass them on to the appropriate method or event handler.

For example, with the following entwine definition

$('a').entwine({
  onclick(e) {
    // eslint-disable-next-line no-console
    console.log('clicked the link element');
  },
});

$('.btn').entwine({
  onclick(e) {
    // eslint-disable-next-line no-console
    console.log('clicked the .btn element');
    this._super(e);
  },
});

Clicking a <a class="btn"></a> element will log this to the console

clicked the .btn element
clicked the link element

If the this._super() call was removed, the event would never be passed on to the handler declared for a.

Limitations

The jQuery object that entwine is called on must be selected using a plain selector, without context. These examples will not work:

$('div', el).entwine(/* ... */);
$([ela, elb, elc]).entwine(/* ... */);
$('<div id="a"></div>').entwine(/* ... */);

Adding methods to DOM elements

To attach methods to DOM nodes, call the entwine function on a jQuery selector object, passing an object listing the method names and bodies.

$('div').entwine({
  foo(args) {
    // Some logic here
  },

  bar(args) {
    // Some logic here
  },
});

Those methods belong to every element which matches the selector. You can then call those methods on any jQuery object for the matched elements, even if you're using a different selector to get the element:

$('.my-div-class').foo();

Any elements in the jQuery selection that match the selector used during definition ('div' in this example) will have foo called with that element set as this. Any other objects are skipped. The return value will be the return value of foo() for the last matched DOM object in the set.

A proper example

Given this DOM structure:

<body>
  <div class="internal_text">Internal text</div>
  <div class="attribute_text" rel="Attribute text"></div>
  <div>Nonsense</div>
</body>

And this entwine definition

$('.internal_text').entwine({
  foo() {
    // eslint-disable-next-line no-console
    console.log(this.text());
  },
});

$('.attribute_text').entwine({
  foo() {
    // eslint-disable-next-line no-console
    console.log(this.attr('rel'));
  },
});

Then this call

$('div').foo();

Will log this to the console

Internal text
Attribute text

Note that it is calling the foo() method on both divs, and that each had a different foo() method defined based on different selectors.

Events

If you declare a function with a name starting with 'on', then instead of defining that function as a callable method, it will be bound to an event of that name. Just like other functions this binding will be live, and only the most specific definition will be used.

<div>Background will turn blue when clicked on</div>
<div>Will also have blue background when clicked on</div>
<div class='green'>Will have green text when clicked on. Background colour will not change</div>
/* No need for onready wrapper. Events are bound as needed */
$('div').entwine({
  onclick() {
    this.css({ backgroundColor: 'blue' });
  },
});

$('.green').entwine({
  onclick() {
    this.css({ color: 'green' });
  },
});

Remember, if you wanted the background colour to change for the div with class green as well, you can simply call this._super() in the click event handler declared for that selector. See Selector specifity and "inheritance" for more information about how this works.

Handling events from other elements

Sometimes we want one element to react to events that are occuring on another element. For these situations, the special from syntax can be used. This should be used sparingly.

Examples of where this can be useful are if the logic for the element the events are happening on is declared in a different file to the logic for the element you want to perform actions on, or if you have extensive API declared for the element you want to perform actions on that would be cumbersome to call from the element that owns the event.

<a>The click event for this element will be handled by the div!</a>
<div class='green'>Will have green text when the link is clicked on.</div>
$('div').entwine({
  'from a': {
    onclick() {
      this.css({ color: 'green' });
      this._super();
    },
  },
});

Constructors / destructors

Declaring a function with the name onmatch will create a behavior that is called on each object when it matches. Likewise, onunmatch will be called when an object that did match this selector stops matching it (because it is removed, or because you've changed its properties).

Note that an onunmatch block must be paired with an onmatch block - an onunmatch without an onmatch in the same entwine definition block is illegal.

You can also declare a function with the name onadd which is similar to onmatch but is explicitly triggered by the element being added to the DOM. This means if the element already exists when you declare this function, your function will not be called (but onmatch would be). Similarly, if you delcare a function called onremove, it will be called when an element is removed from the DOM. This does not need an onadd function to be declared, unlike onunmatch.

The onmatch and onadd events are triggered asynchronously - this means that after you add an element to the DOM, it is not guaranteed that functionality in your onmatch or onadd function for that element will be processed immediately. This is handled using a MutationObserver.

The onunmatch and onremove events are triggered synchronously however, so you can rely on the element still existing when these functions are called. The element will not be removed from the DOM until the onunmatch and onremove functions for the element have been called and finished executing.

Properties

Entwine has a special concept of properties. You can declare a property for a given selector, and a getter and setter method will be implicitly created for it. Properties are declared by setting and word starting with a capital letter, like so:

$('div').entwine({
  MyProperty: 'some value',
});

You can get and set the property by calling a method with get and set before the property name:

$('div').getMyProperty(); // returns 'some value'
$('div').setMyProperty(32);
$('div').getMyProperty(); // returns 32

Namespaces

Most entwine logic defined in core Silverstripe CMS modules uses the ss namespace.

To avoid name clashes, to allow multiple bindings to the same event, and to generally seperate a set of functions from other code, you can use namespaces. These are declared by calling the jQuery.entwine() function and passing in both the namespace name and a callback, which contains all entwine declarations which belong to that namespace:

$.entwine('foo.bar', ($) => {
  $('div').entwine({
    baz() {
      // Some logic here
    }
  });
});

You can then call these functions like this:

$('div').entwine('foo.bar').baz();

Notice that $ is passed in as an argument to the callback function. This is a different object than the $ which the entwine() function is being called on, which contains information about the namespace that you have defined. Another way to write the namespace closure, which illustrates this point, would be like so:

jQuery.entwine('foo.bar', ($) => {
  $('div').entwine({
    // declarations here
  });
});

Namespaced functions, properties, and event handlers work just like regular functions (this is still set to a matching DOM Node). However, specifity is calculated per namespace. This is particularly useful for events, because given this:

$('div').entwine({
  onclick() {
    this.css({ backgroundColor: 'blue' });
  },
});

$.entwine('foo', ($) => {
  $('div').entwine({
    onclick() {
      this.css({ color: 'green' });
    },
  });
});

Clicking on a div will change the background and foreground color.

This is particularly important when writing reusable code, since otherwise you can't know before hand whether your event handler will be called or not

Although a namespace can be any string, best practise is to name them with dotted-identifier notation. For example, the entwine logic for controlling the preview panel in the CMS uses the ss.preview namespace.

Namespaces and scope (or what the hell's up with that ugly function closure)

Inside a namespace definition, functions remember the namespace they are in, and calls to other functions will be looked up inside that namespace first. Where they don't exist (see warning below), they will be looked up in the base namespace

$.entwine('foo', ($) => {
  $('div').entwine({
    bar() {
      this.baz();
      this.qux();
    },
    baz() {
      // eslint-disable-next-line no-console
      console.log('baz');
    },
  });
});

$('div').entwine({
  qux() {
    // eslint-disable-next-line no-console
    console.log('qux');
  },
});

With the above entwine declarations, calling

Note that trying to call $('div').bar(); would throw an uncaught TypeError saying something like "$(...).bar is not a function", because the bar() function was defined in a namespace, but we are trying to call that function from outside of that namespace.

$('div').entwine('foo').bar();

Will print this to the console:

baz
qux

Note that 'exists' means that a function is declared in this namespace for any selector, not just a matching one. Given the dom

<div>Internal text</div>

And the entwine definitions

$.entwine('foo', ($) => {
  $('div').entwine({
    bar() {
      this.baz();
    },
  });

  $('span').entwine({
    baz() {
      // eslint-disable-next-line no-console
      console.log('a');
    },
  });
});

$('div').entwine({
  baz() {
    // eslint-disable-next-line no-console
    console.log('b');
  },
});

Then calling $('div')entwine('foo').bar(); will not display "b". Even though the span rule could never match a div, because baz() is defined for some rule in the foo namespace, the base namespace will never be checked.

Calling to another namespace (and forcing base)

Inside a namespace, namespace lookups are by default relative to the current namespace.

In some situations (such as the last example) you may want to force using the base namespace. In this case you can call entwine with the first argument being the base namespace code '.'. For example, if the first definition in the previous example was

$.entwine('foo', ($) => {
  $('div').entwine({
    bar() {
      this.entwine('.').baz();
    },
  });
});

Then "b" would be output to the console.

Nesting namespace blocks

You can also nest namespace declarations. In this next example, we're defining the functions $().entwine('zap').bar() and $().entwine('zap.pow').baz()

jQuery.entwine('zap', ($) => {
  $('div').entwine({
    bar() {
      // Some logic here
    },
  });

  $.entwine('pow', ($jq) => {
    $jq('div').entwine({
      baz() {
        // Some logic here
      },
    });
  });
});

Using

Sometimes a block outside of a namespace will need to refer to that namespace repeatedly. By passing a function (instead of an object) to the entwine function, you can change the looked-up namespace.

$('div').entwine('foo', function ($) {
  this.bar();
  this.bar();
  this.bar();
});

would be the equivalent of

const div = $('div').entwine('foo');
div.bar();
div.bar();
div.bar();

Both of the above implementations repeatedly call the bar() method which was declared in the foo entwine namespace on the element matching div.

This is equivalent to the (deprecated) with feature in JavaScript. Care should be taken to only use this construct in situations that merit it.

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