gitlab-org--gitlab-foss/doc/development/fe_guide/design_patterns.md

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Design Patterns

Singletons

When exactly one object is needed for a given task, prefer to define it as a class rather than as an object literal. Prefer also to explicitly restrict instantiation, unless flexibility is important (e.g. for testing).

// bad

const MyThing = {
  prop1: 'hello',
  method1: () => {}
};

export default MyThing;

// good

class MyThing {
  constructor() {
    this.prop1 = 'hello';
  }
  method1() {}
}

export default new MyThing();

// best

export default class MyThing {
  constructor() {
    if (!MyThing.prototype.singleton) {
      this.init();
      MyThing.prototype.singleton = this;
    }
    return MyThing.prototype.singleton;
  }

  init() {
    this.prop1 = 'hello';
  }

  method1() {}
}

Manipulating the DOM in a JS Class

When writing a class that needs to manipulate the DOM guarantee a container option is provided. This is useful when we need that class to be instantiated more than once in the same page.

Bad:

class Foo {
  constructor() {
    document.querySelector('.bar');
  }
}
new Foo();

Good:

class Foo {
  constructor(opts) {
    document.querySelector(`${opts.container} .bar`);
  }
}

new Foo({ container: '.my-element' });

You can find an example of the above in this class;