javascript - For .. in loop? -

i'm losing here.. extremely confused how loop works.

from w3 schools:

var person={fname:"john",lname:"doe",age:25};   (x in person) { document.write(person[x] + " "); } 

person object properties right? how properties being accessed brackets? thought arrays?

why work, , shouldn't this?:

var person=[];  person["fname"] = "john"; person["lname"] = "doe"; person["age"] = "25";   (x in person) { document.write(person[x] + " "); } 

there 2 ways in have access object's properties:

• obj.key
• obj['key']

the advantage of second method can provide key dynamically, e.g. obj[x] in example. obj.x literally mean x property (i.e. obj['x']), not want.

arrays work brackets, brackets not limited arrays. arrays under hood objects, designed numeric keys. can still add properties non-numeric keys them, that's not designed for.