Object.defineProperty

It allows us to define a property in an existing object using a property descriptor.

var obj = { };

Object.defineProperty(obj, 'foo', { value: 'foo' });

console.log(obj.foo);

Console output

foo

Object.defineProperty can be called with the following options:

Object.defineProperty(obj, 'nameOfTheProperty', {
  value: valueOfTheProperty, 
  writable: true, // if false, the property is read-only
  configurable : true, // true means the property can be changed later
  enumerable : true // true means property can be enumerated such as in a for..in loop
});

Object.defineProperties allows you to define multiple properties at a time.

var obj = {};
Object.defineProperties(obj, {
  property1: {
    value: true,
    writable: true
  },
  property2: {
    value: 'Hello',
    writable: false
  }      
});

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