78 lines
1.4 KiB
Markdown
78 lines
1.4 KiB
Markdown
# Design Patterns
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## Singletons
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When exactly one object is needed for a given task, prefer to define it as a
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`class` rather than as an object literal. Prefer also to explicitly restrict
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instantiation, unless flexibility is important (e.g. for testing).
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```javascript
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// bad
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const MyThing = {
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prop1: 'hello',
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method1: () => {}
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};
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export default MyThing;
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// good
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class MyThing {
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constructor() {
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this.prop1 = 'hello';
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}
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method1() {}
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}
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export default new MyThing();
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// best
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export default class MyThing {
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constructor() {
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if (!this.prototype.singleton) {
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this.init();
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this.prototype.singleton = this;
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}
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return this.prototype.singleton;
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}
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init() {
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this.prop1 = 'hello';
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}
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method1() {}
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}
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```
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## Manipulating the DOM in a JS Class
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When writing a class that needs to manipulate the DOM guarantee a container option is provided.
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This is useful when we need that class to be instantiated more than once in the same page.
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Bad:
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```javascript
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class Foo {
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constructor() {
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document.querySelector('.bar');
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}
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}
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new Foo();
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```
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Good:
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```javascript
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class Foo {
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constructor(opts) {
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document.querySelector(`${opts.container} .bar`);
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}
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}
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new Foo({ container: '.my-element' });
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```
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You can find an example of the above in this [class][container-class-example];
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[container-class-example]: https://gitlab.com/gitlab-org/gitlab-ce/blob/master/app/assets/javascripts/mini_pipeline_graph_dropdown.js
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