Objects

Objects

  • 3.1 Use the literal syntax for object creation. eslint: no-new-object

    // bad
    const item = new Object();
    
    // good
    const item = {};
    
  • 3.2 Use computed property names when creating objects with dynamic property names.

    Why? They allow you to define all the properties of an object in one place.

    
    function getKey(k) {
      return `a key named ${k}`;
    }
    
    // bad
    const obj = {
      id: 5,
      name: 'San Francisco',
    };
    obj[getKey('enabled')] = true;
    
    // good
    const obj = {
      id: 5,
      name: 'San Francisco',
      [getKey('enabled')]: true,
    };
    
  • 3.3 Use object method shorthand. eslint: object-shorthand jscs: requireEnhancedObjectLiterals

    // bad
    const atom = {
      value: 1,
    
      addValue: function (value) {
        return atom.value + value;
      },
    };
    
    // good
    const atom = {
      value: 1,
    
      addValue(value) {
        return atom.value + value;
      },
    };
    
  • 3.4 Use property value shorthand. eslint: object-shorthand jscs: requireEnhancedObjectLiterals

    Why? It is shorter to write and descriptive.

    const lukeSkywalker = 'Luke Skywalker';
    
    // bad
    const obj = {
      lukeSkywalker: lukeSkywalker,
    };
    
    // good
    const obj = {
      lukeSkywalker,
    };
    
  • 3.5 Group your shorthand properties at the beginning of your object declaration.

    Why? It’s easier to tell which properties are using the shorthand.

    const anakinSkywalker = 'Anakin Skywalker';
    const lukeSkywalker = 'Luke Skywalker';
    
    // bad
    const obj = {
      episodeOne: 1,
      twoJediWalkIntoACantina: 2,
      lukeSkywalker,
      episodeThree: 3,
      mayTheFourth: 4,
      anakinSkywalker,
    };
    
    // good
    const obj = {
      lukeSkywalker,
      anakinSkywalker,
      episodeOne: 1,
      twoJediWalkIntoACantina: 2,
      episodeThree: 3,
      mayTheFourth: 4,
    };
    
  • 3.6 Only quote properties that are invalid identifiers. eslint: quote-props jscs: disallowQuotedKeysInObjects

    Why? In general we consider it subjectively easier to read. It improves syntax highlighting, and is also more easily optimized by many JS engines.

    // bad
    const bad = {
      'foo': 3,
      'bar': 4,
      'data-blah': 5,
    };
    
    // good
    const good = {
      foo: 3,
      bar: 4,
      'data-blah': 5,
    };
    
  • 3.7 Do not call Object.prototype methods directly, such as hasOwnProperty, propertyIsEnumerable, and isPrototypeOf.

    Why? These methods may be shadowed by properties on the object in question - consider { hasOwnProperty: false } - or, the object may be a null object (Object.create(null)).

    // bad
    console.log(object.hasOwnProperty(key));
    
    // good
    console.log(Object.prototype.hasOwnProperty.call(object, key));
    
    // best
    const has = Object.prototype.hasOwnProperty; // cache the lookup once, in module scope.
    /* or */
    import has from 'has';
    // ...
    console.log(has.call(object, key));
    
  • 3.8 Prefer the object spread operator over Object.assign to shallow-copy objects. Use the object rest operator to get a new object with certain properties omitted.

    // very bad
    const original = { a: 1, b: 2 };
    const copy = Object.assign(original, { c: 3 }); // this mutates `original` ಠ_ಠ
    delete copy.a; // so does this
    
    // bad
    const original = { a: 1, b: 2 };
    const copy = Object.assign({}, original, { c: 3 }); // copy => { a: 1, b: 2, c: 3 }
    
    // good
    const original = { a: 1, b: 2 };
    const copy = { ...original, c: 3 }; // copy => { a: 1, b: 2, c: 3 }
    
    const { a, ...noA } = copy; // noA => { b: 2, c: 3 }
    

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