【JavaScript Inheritance】
1、Inheriting properties
JavaScript objects are dynamic "bags" of properties (referred to as own properties). JavaScript objects have a link to a prototype object. When trying to access a property of an object, the property will not only be sought on the object but on the prototype of the object, the prototype of the prototype, and so on until either a property with a matching name is found or the end of the prototype chain is reached.
// Let's assume we have object o, with its own properties a and b: // {a: 1, b: 2} // o.[[Prototype]] has properties b and c: // {b: 3, c: 4} // Finally, o.[[Prototype]].[[Prototype]] is null. // This is the end of the prototype chain, as null, // by definition, has no [[Prototype]]. // Thus, the full prototype chain looks like: // {a: 1, b: 2} ---> {b: 3, c: 4} ---> null console.log(o.a); // 1 // Is there an 'a' own property on o? Yes, and its value is 1. console.log(o.b); // 2 // Is there a 'b' own property on o? Yes, and its value is 2. // The prototype also has a 'b' property, but it's not visited. // This is called "property shadowing." console.log(o.c); // 4 // Is there a 'c' own property on o? No, check its prototype. // Is there a 'c' own property on o.[[Prototype]]? Yes, its value is 4. console.log(o.d); // undefined // Is there a 'd' own property on o? No, check its prototype. // Is there a 'd' own property on o.[[Prototype]]? No, check its prototype. // o.[[Prototype]].[[Prototype]] is null, stop searching, // no property found, return undefined.