javascript - property access using [] array notation -

i newbie js. reading definite guide , came through this, created player object this

   var player= {     name: 'the player',     age: 33,     address:'street 32' }  var addr = ""; (i = 0; < 4; i++) {     addr += player["address" + i] + '\n'; } 

now book says loop add code reads , concatenates address0, address1, address2, , address3 properties of player object. not working..

to add 1 address property player object like

player.address = "some street 32"; 

if want add 4 "address fields"/ properties player object:

var player={     name: 'the player',     age: 33 };  (i = 0; < 4; i++) {     player["address" + i] = "empty"; }   console.log( player ); 

_{[object object] {
  address0: "empty",
  address1: "empty",
  address2: "empty",
  address3: "empty",
  age: 33,
  name: "the player"
}}

though see no use-case of pre-creating properties you'll not use in future. rather create array of addresses (if need store more addresses) like:

player = {   addresses = [],   name = "the player" } 

than whenever need add new address player like:

player.addresses.push("street 32"); player.addresses.push("newstreet 43");  console.log( player.addresses );    // ["street 32", "newstreet 43"] console.log( player.addresses[0] ); // "street 32" 

than whenever want addresses can loop player.addresses or if want newest address (the latest 1 in array) do:

var playerlatestaddress = player.addresses.slice(-1).pop(); // "mynew, street 43" 

---

instead code does:

var addr = "";            // create empty string concatenate (i = 0; < 4; i++) { // 4 times....     // add `addr` value existent `player.addressn` property     addr += player["address" + i] + '\n'; // error: player.address0 undefined } 

therefore if test console.log( addr ) you'll get:

_{"undefined
undefined
undefined
undefined
"}