Decide on and document a convention for singletons
> The singleton pattern is a design pattern that restricts the instantiation of a class to one object. This is useful when exactly one object is needed to coordinate actions across the system.
The simplest implementation uses an object literal to contain the logic.
```javascript
gl.MyThing = {
prop1: 'hello',
method1: () => {}
};
```
A live example of this is [GfmAutoComplete](172aab108b/app/assets/javascripts/gfm_auto_complete.js.es6)
Another approach makes use of ES6 `class` syntax.
```javascript
let singleton;
class MyThing {
constructor() {
if (!singleton) {
singleton = this;
singleton.init();
}
return singleton;
}
init() {
this.prop1 = 'hello';
}
method1() {}
}
gl.MyThing = MyThing;
```
A live example of this is [Sidebar](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/app/assets/javascripts/sidebar.js.es6)
Another functional approach to define Singleton using `Javascript Revealing Module Pattern` is like below
```javascript
/**
* 1. It instantiates only a single object
* 2. It is safe – it keeps the reference to the singleton inside a variable, which lives inside a lexical closure, so it is not accessible by the outside world
* 3. It allows privacy – you can define all private methods of your singleton inside the lexical closure of the first module pattern
* 4. No this keyword trap (no wrong context referring)
* 5. No use of new keyword
* 6. Easy to write test code
*/
//
const Singleton = (function () {
// Instance stores a reference to the Singleton
var instance;
function init() {
// Singleton
// Private methods and variables
function privateMethod(){
console.log( "I am private" );
}
var privateVariable = "Im also private";
var privateRandomNumber = Math.random();
return {
// Public methods and variables
publicMethod: function () {
console.log( "The public can see me!" );
},
publicProperty: "I am also public",
getRandomNumber: function() {
return privateRandomNumber;
}
};
};
return {
// Get the Singleton instance if one exists
// or create one if it doesn't
getInstance: function () {
if ( !instance ) {
instance = init();
}
return instance;
}
};
})();
const singletonObj = Singleton.getInstance()
```
## Are there points in the code the reviewer needs to double check?
## What does this MR do?
Creates a space for discussion and contribution for interested devs.
## Why was this MR needed?
## Screenshots (if relevant)
## Does this MR meet the acceptance criteria?
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [x] All builds are passing
(http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)
## What are the relevant issue numbers?
See merge request !6620
Add ES array methods as cause of Phantom.js errors.
## What does this MR do?
Adds another example of something that causes a common error in JavaScript testing to the frontend dev docs.
See merge request !7102
Filipa Lacerda
Jacob Schatz
Bryce Johnson
Clement Ho
Nur Rony
Jacob Schatz
Sam Rose
Fatih Acet
Winnie
Connor Shea