Effective JavaScript Item 39 never reuse property names in a parent type

this series as effective JavaScript 's reading notes.

Suppose you need to Item in the Actor object to join a ID Information:

function Actor (scene, X, y) {this.scene = Scene;this.x = X;this.y = Y;this.id = ++actor.nextid;scene.register (this);} Actor.nextid = 0;

at the same time. You also need to include the ID information in the Actor 's subtype Alien :

function Alien (scene, X, y, direction, speed, strength) {Actor.call (this, scene, X, y); this.direction = Direction;this.spe ed = Speed;this.strength = Strength;this.damage = 0;this.id = ++alien.nextid; Conflicts with actor id!} Alien.nextid = 0;

in alien Also in the constructor of id property was assigned. So. In alien id property is always passed alien.nextid actor.nextid .

The ID property of the parent type overrides the ID property of the quilt type .

The workaround is also very easy, using different property names in different types:

function Actor (scene, X, y) {this.scene = Scene;this.x = X;this.y = Y;this.actorid = ++actor.nextid;//distinct from Alie Nidscene.register (this);} Actor.nextid = 0;function Alien (scene, X, y, direction, speed, strength) {Actor.call (this, scene, X, y); this.direction = d Irection;this.speed = Speed;this.strength = Strength;this.damage = 0;this.alienid = ++alien.nextid; Distinct from actorid}alien.nextid = 0;

Summarize

1. Note the attribute names that are used in all parent types do not and are repeated in subtypes.
2. Do not reuse property names that are already used in the parent type in subtypes.

Effective JavaScript Item 39 never reuse property names in a parent type