No new

Use the literal syntax for object creation.

ESLint: no-new-object

Examples

⇣ Incorrect code for this rule:

const snow = new Object();

⇡ Correct code for this rule:

const snow = {};

ES6 Computed Properties

Use computed property names when creating objects with dynamic property names. They allow to define all the properties of an object in one place.

Examples

⇣ Incorrect code for this rule:

function getSnow(snow) {
  return `a key named ${snow}`;
}

const obj = {
  id: 5,
  name: "South Pole"
};
obj[getSnow("enabled")] = true;

⇡ Correct code for this rule:

function getSnow(snow) {
  return `a key named ${snow}`;
}

const obj = {
  id: 5,
  name: "South Pole",
  [getSnow("enabled")]: true
};

ES6 Object Shorthand

Use object method shorthand.

ESLint: object-shorthand

Examples

⇣ Incorrect code for this rule:

const snow = {
  flake: 1,

  addFlake: function(flake) {
    return snow.flake + flake;
  }
};

⇡ Correct code for this rule:

const snow = {
  flake: 1,

  addFlake(flake) {
    return snow.flake + flake;
  }
};

ES6 Object Concise

Use property value shorthand. It is shorter to write and descriptive.

ESLint: object-shorthand

Examples

⇣ Incorrect code for this rule:

const southPole = "South Pole";

const obj = {
  southPole: southPole
};

⇡ Correct code for this rule:

const southPole = "South Pole";

const obj = {
  southPole
};

Grouped Shorthand

Group shorthand properties at the beginning of object declarations. It is easier to tell which properties are using the shorthand.

Examples

⇣ Incorrect code for this rule:

const southPole = "South Pole";
const northPole = "North Pole";

const obj = {
  floatingIce: 1,
  northPole,
  penguins: 2,
  southPole
};

⇡ Correct code for this rule:

const southPole = "South Pole";
const northPole = "North Pole";

const obj = {
  northPole,
  southPole,
  floatingIce: 1,
  penguins: 2
};

Quoted Properties

Only quote properties that are invalid identifiers. In general we consider it subjectively easier to read. It improves syntax highlighting and is also more easily optimized by many JS engines.

ESLint: quote-props

Examples

⇣ Incorrect code for this rule:

const obj = {
  "snow": 1,
  "ice": 2
  "frost-wind": 3
};

⇡ Correct code for this rule:

const obj = {
  snow: 1,
  ice: 2,
  "frost-wind": 3
};

Prototype Builtins

Do not call Object.prototype methods directly, such as hasOwnProperty, propertyIsEnumerable, and isPrototypeOf. 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)).

Examples

⇣ Incorrect code for this rule:

console.log(object.hasOwnProperty(key));

⇡ Correct code for this rule:

console.log(Object.prototype.hasOwnProperty.call(object, key));

⇢ Recommended code for this rule:

// Cache the lookup once, in module scope.
const hasProp = Object.prototype.hasOwnProperty;

console.log(hasProp.call(object, key));

Using the has npm package:

import has from "has";

console.log(has.call(object, key));

Rest Spread

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.

Examples

↯ Critical incorrect code for this rule:

const original = {
  snow: 1,
  ice: 2
};
// Both statements mutate "original"!
const copy = Object.assign(original, { frost: 3 });
delete copy.snow; // so does this

⇣ Incorrect code for this rule:

const original = { snow: 1, ice: 2 };
const copy = Object.assign({}, original, { frost: 3 });
console.log(copy); // { snow: 1, ice: 2, frost: 3 }

⇡ Correct code for this rule:

const original = { snow: 1, ice: 2 };
const copy = { ...original, frost: 3 };
console.log(copy); // { snow: 1, ice: 2, frost: 3 }

const { snow, ...noSnow } = copy;
console.log(noSnow); // { ice: 2, frost: 3 }

⇢ Recommended code for this rule:

// Cache the lookup once, in module scope.
const has = Object.prototype.hasOwnProperty;

console.log(has.call(object, key));

Using the has npm package:

import has from "has";

console.log(has(object, key));