[JavaScript]“类”与“继承”

var a = {
    x:10,
    calculate:function(z){
        return this.x+this.y+z;
    }
}
var b = {
    y:20,
    __proto__:a // b extends a 
}
var c = {
    y:30,
    __proto__:a
}
//call the inherited method
b.calculate(3); // 10+20+3 = 33
c.calculate(3); // 10+30+3 = 43

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The rule is simple: if a property or a method is not found in the object itself (i.e. the object has no such an *own *property), then there is an attempt to find this property/method in the prototype chain. If the property is not found in the prototype, then a prototype of the prototype is considered, and so on, i.e. the whole prototype chain (absolutely the same is made in class-based inheritance, when resolving an inherited *method *— there we go through the class chain). The first found property/method with the same name is used. Thus, a found property is called *inherited *property. If the property is not found after the whole prototype chain lookup, then undefined value is returned.

JavaScripte有种很明显的“链式逻辑”，当前对象/作用域找不到引用的属性或者方法，则沿着链向上寻找，此处是在 b对象 中没有找到calculate方法，则沿着“原型链（prototype/class chain）”向上寻找，在 a对象 里找到了calculate方法...，在调用过程中，会沿着链依次寻找到最近的名称相同属性或者方法并使用（The first found property/method with the same name is used）。如果没有找到，则返回 undefined

prototype chain