ngbindonce

ngBindonce
========

High performance binding for AngularJs

Usage

* npm install ngBindonce --save
* Include the ngBindonce.js script provided by this component into your app.
* Add 'ng.bindonce' as a module dependency to your app: angular.module('app', ['ng.bindonce'])

Demo

Here is an example of how AngularJs can freeze your UI, try to press and hold a key inside the input field, when the table is filled with only 1 person everything is ok, you can see how the DOM is updated by the input in real time, however if you try to load 1000 person (or even 500 if the testing device is not powerfull) and repeat the experiment you can see how the UI is frozen. In this other demo ngBindonce will take care of your watchers and the UI will be reactive as it should be. The code is the same for both demos, the only difference is that I replaced any ng- tag inside the table with the equivalent bo- tag.

Overview

AngularJs provides a great data binding system but if you abuse of it the page can run into some performance issues, it's known that more of 2000 watchers can lag the UI and that amount can be reached easily if you don't pay attention to the data-binding. Sometime you really need to bind your data using watchers, especially for SPA because the data are updated in real time, but often you can avoid it with some efforts, most of the data presented in your page, once rendered, are immutable so you shouldn't keep watching them for changes.

For instance, take a look to this snippet:
``html


• 
  
  
  
  
  


`
Angular internally creates a $watch for each ng- directive in order to keep the data up to date, so in this example just for displaying few info it creates 6 + 1 (ngRepeatWatch)* watchers per person, even if the person is supposed to remain the same once shown. Iterate this amount for each person and you can have an idea about how easy is to reach 2000 watchers. Now if you need it because those data could change while you show the page or are bound to some models, it's ok. But most of the time they are static data that don't change once rendered. This is where ngBindonce can really help you.

The above example done with ngBindonce:
`html


• 
  
  
  
  
  


`
Now this example uses 0 watches per person and renders exactly the same result as the above that uses ng-. (Angular still uses 1 watcher for ngRepeatWatch)*

$3

OK until here nothing completely new, with a bit of efforts you could create your own directive and render the person inside the link function, or you could use watch fighters that has a similar approach, but there is still one problem that you have to face and ngBindonce already handles it: the existence of the data when the directive renders the content. Usually the directives, unless you use watchers or bind their attributes to the scope (still a watcher), render the content when they are loaded into the markup, but if at that given time your data is not available, the directive can't render it. ngBindonce can wait until the data is ready before to rendering the content.
Let's take a look at the follow snippet to better understand the concept:
`html


...

`
This basic directive works as expected, it renders the Person data without using any watchers. However, if Person is not yet available inside the $scope when the page is loaded (say we get Person via $http or via $resource), the directive is useless, scope.$eval(attr.myCustomSetText) simply renders nothing and exits.

Here is how we can solve this issue with ngBindonce:
`html



`
ngBindonce="Person" does the trick, any bo- attribute belonging to ngBindonce waits until the parent ngBindonce="{somedata}" is validated and then renders its content. Once the scope contains the value Person then each bo- child gets filled with the proper values. In order to accomplish this task, ngBindonce uses just one temporary watcher, no matters how many children need to be rendered. As soon as it gets Person the watcher is promptly removed. If the $scope already contains the data ngBindonce is looking for, then it doesn't create the temporary watcher and simply starts rendering its children.

You may have noticed that the first example didn't assign any value to the ngBindonce attribute:
`html




• 
...
`
when used with ng-repeat ngBindonce doesn't need to check if person is defined because ng-repeat creates the directives only when person exists. You could be more explicit:
• , however assigning a value to ngBindonce in an ng-repeat won't make any difference.

  $3

  
  Some directives (ng-href, ng-src) use interpolation, ie: ng-href="/profile/{{User.profileId}}".
Both ng-href and ng-src have the bo-* equivalent directives: bo-href-i and bo-src-i (pay attention to the -i, it stands for interpolate). As expected they don't use watchers however Angular creates one watcher per interpolation, for instance bo-href-i="/profile/{{User.profileId}}" sets the element's href once, as expected, but Angular keeps a watcher active on {{User.profileId}} even if bo-href-i doesn't use it.
That's why by default the bo-href doesn't use interpolation or watchers. The above equivalent with 0 watchers would be bo-href="'/profile/' + User.profileId". Nevertheless, bo-href-i and bo-src-i are still maintained for compatibility reasons.

  $3

  
  Almost every bo- directive replace the equivalent ng- and works in the same ways, except it is evaluated once.
Consequentially you can use any valid angular expression, including filters. This is an example how to use a filter:
`html
  
  
  
  
  
  `

  Attribute Usage

  
  | Directive | Description | Example |
  |------------|----------------|-----|
  | ngBindonce="{somedata}"| ngBindonce is the main directive. {somedata} is optional, and if present, forces ngBindonce to wait until somedata is defined before rendering its children |
  ...

  |
| bo-if = "condition" | equivalent to ng-if but doesn't use watchers ||
| bo-switch = "expression" | equivalent to ng-switch but doesn't use watchers |

  public private

  |
| bo-show = "condition" | equivalent to ng-show but doesn't use watchers ||
| bo-hide = "condition" | equivalent to ng-hide but doesn't use watchers ||
| bo-disabled = "condition" | equivalent to ng-disabled but doesn't use watchers ||
| bo-text = "text" | evaluates "text" and print it as text inside the element | |
| bo-bind = "text" | alias for bo-text, equivalent to ng-bind but doesn't use watchers | |
| bo-html = "markup" | evaluates "markup" and render it as html inside the element |bo-html="Person.description"|
| bo-href-i = "url"
use bo-href instead | equivalent to ng-href.
Heads up! Using interpolation {{}} it creates one watcher:
bo-href-i="/p/{{Person.id}}".
Use bo-href to avoid the watcher:
bo-href="'/p/' + Person.id" ||
| bo-href = "url" | similar to ng-href but doesn't allow interpolation using {{}} like ng-href.
Heads up! You can't use interpolation {{}} inside the url, use bo-href-i for that purpose |
or
|
| bo-src-i = "url"
use bo-src instead | equivalent to ng-src.
Heads up! It creates one watcher ||
| bo-src = "url" | similar to ng-src but doesn't allow interpolation using {{}} like ng-src.
Heads up! You can't use interpolation {{}}, use bo-src-i for that purpose ||
| bo-class = "object/string" | equivalent to ng-class but doesn't use watchers ||
| bo-alt = "text" | evaluates "text" and render it as alt for the element ||
| bo-title = "text" | evaluates "text" and render it as title for the element ||
| bo-id = "#id" | evaluates "#id" and render it as id for the element ||
| bo-style = "object" | equivalent to ng-style but doesn't use watchers ||
| bo-value = "expression" | evaluates "expression" and render it as value for the element ||
| bo-attr bo-attr-foo = "text" | evaluates "text" and render it as a custom attribute for the element |

  |

  Build

  
  `
$ gulp
``

  Thanks to all the contributors

  LICENSE - "MIT License"

  Copyright (c) 2013-2014 Pasquale Vazzana

  Permission is hereby granted, free of charge, to any person obtaining a copy
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  copies of the Software, and to permit persons to whom the Software is
  furnished to do so, subject to the following conditions:

  The above copyright notice and this permission notice shall be included in
  all copies or substantial portions of the Software.

  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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  THE SOFTWARE.
  

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