Here is an ES5 object literal with two string properties and a function property:

let user = { 
  firstName: 'Max',
  lastName: 'Muster',
  fullName: function() { return this.firstName + ' ' + this.lastName }
}

user.fullName() // => 'Max Muster'

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In ES6 we can define a function property using the following shorthand syntax:

let user = { 
  firstName: 'Max',
  lastName: 'Muster',
  fullName() { return this.firstName + ' ' + this.lastName }
}

user.fullName() // => 'Max Muster'

We can also define a getter inside the object literal, without using Object.defineProperty():

let user = { 
  firstName: 'Max',
  lastName: 'Muster',
  get fullName() { return this.firstName + ' ' + this.lastName }
}

user.fullName // no parentheses