JavaScript 1.8.1 note

Starting in JavaScript 1.8.1, setters are no longer called when setting properties in object and array initializers.

JavaScript 1.8.5 note

Starting in JavaScript 1.8.5, set operator:

• can have an identifier which is either a number or a string;
• must have exactly one parameter (see Incompatible ES5 change: literal getter and setter functions must now have exactly zero or one arguments for more information);
• must not appear in an object literal with another set or with a data entry for the same property ({ set x(v) { }, set x(v) { } } and { x: ..., set x(v) { } } are forbidden).

Defining a setter with the set operator

This will define a pseudo-property current of object o that, when assigned a value, will update log with that value:

var o = {
  set current (str) {
    return this.log[this.log.length] = str;
  },
  log: []
}

Note that current is not defined and any attempts to access it will result in undefined

Removing a setter with the delete operator

delete o.current;