Javascript copy semantics

Question

the following is the normal javascript semantics:

js> a={'a':{'red':12,'green':23,'blue':34}}
({a:{red:12, green:23, blue:34}})
js> b=a['a']                                                                    
({red:12, green:23, blue:34})
js>b={red:122, green:232, blue:142}                                                                        
({red:122, green:232, blue:142})
js> a
({a:{red:12, green:23, blue:34})
js>

the following is the semantics I would like to have:

js> a={'a':{'red':12,'green':23,'blue':34}}
({a:{red:12, green:23, blue:34}})
js> b=a['a']                                                                    
({red:12, green:23, blue:34})
js>b={red:122, green:232, blue:142}                                                                        
({red:122, green:232, blue:142})
js> a
({red:122, green:232, blue:142})
js>

is there any simple inner trick to make javascript to behave my way?

Answer 1

Javascript doesn't have "pointer to a reference" types. However, you can create a "property of an object" type (object, property name; cannot point to a local variable).

a={'a':{'red':12,'green':23,'blue':34}}
//({a:{red:12, green:23, blue:34}})
b={obj:a, key:"a"}
b.obj[b.key]                                                             
//({red:12, green:23, blue:34})
b.obj[b.key]={red:122, green:232, blue:142}                                                                        
//({red:122, green:232, blue:142})
a
//({a:{red:122, green:232, blue:142}})

alternatively, you could overwrite the object b refers to:

a={'a':{'red':12,'green':23,'blue':34}}
//({a:{red:12, green:23, blue:34}})
b=a['a'] //or a.a
//({red:12, green:23, blue:34})
b.red = 122;
b.green = 232;
b.blue = 142;
b
//({red:122, green:232, blue:142})
a
//({a:{red:122, green:232, blue:142}})