How to create an array like object in javascrript

Question

Here is what I need:

var user = {
    'White' : 24,
    'Jack'  : 25,
    'Jone'  : 24,
    ……
}

In this obj, I want to store name and age of a person. And the obj can only store 10 person. If the 11th person is added, the first person should be delete. So I'm thinking of an array, the unshift and pop method:

var user = [
    {'White': 24},
    {'Jack' : 25},
    {'Jone' : 24},
    ……
]
user.unshif({'Bob': 24});
if(user.length>10){user.pop()};

This works fine except one problem. When I want to know White's age, I must use a loop:

for(var i=0; i<user.length; i++){
    ……
}

I don't think it's a good method. is there any array-like object that can meet the needs. And here is what I do:

function arrayObj(){
    var arr = [], obj = {};
    this.pop = function(){
        var o = arr.pop();
        if(o){
            for(var k in o){ delete obj[k]; }
            this.length--;
        }
    };
    this.unshift = function(o){
        arr.unshift(o);
        for(var k in o){ obj[k] = o[k]; }
        this.length++;
    };
    this.length = 0;
    this.get = function(n){
        if(obj[n]!=null && obj[n]!=undefined){
            return obj[n];
        } else {
            return null;
        }
    };
}
var user = new arrayObj();

Answer 1

Basically what you want is the constant look up speed of a hash table object, but to have the simple ordered structure of an array. Reasonable enough.

The solution I thought of was to use a JavaScript object (hash table basically) to keep track of the indexes at which the person objects are stored on an array. It's not concise but a bit verbose so as to increase readability. Also it doesn't have any error checking but that should be easy enough to add. http://jsfiddle.net/7es2xwqx/

function HashArray(){
    this.indexKeys = {};
    this.storage = [];
}

HashArray.prototype.addUser = function(name, age){
    //if length is 10, storage.shift(), and delete
    //     delete user from indexKeys
    if (this.storage.length === 10) {
       this.storage.shift();
       delete this.indexKeys[name];
    }

    // add user object {name, age} to storage
    // add index of object on storage to indexKeys
    // as {name: indexOnStorage}

    this.indexKeys[name] = this.storage.length;
    this.storage.push({name:name, age:age});
};

HashArray.prototype.getPerson = function(name){
    var indexPersonObjLocated = this.indexKeys[name];
    return this.storage[indexPersonObjLocated];
};
HashArray.prototype.getStorage = function(){
    return this.storage;
};
HashArray.prototype.getKeys = function(){
    return this.indexKeys;
};

var coolObj = new HashArray();
coolObj.addUser("White", 24);
coolObj.addUser("Whate", 25);
coolObj.addUser("Plite", 26);
console.log(coolObj.getUser("White"));
console.log(coolObj.getUser("Whate"));
console.log(coolObj.getUser("Plite"));

Answer 2

function obj()
{
  this.__model = [];
}

obj.prototype.add = function(key, value)
{
  this[key] = value;
  this.__model.push({ key: key, value: value });
  if(this.__model.length > 10)
    delete this[this.__model.shift().key];

  console.log(this);
}

http://plnkr.co/edit/dxbiXj5y3e3uiu0Hch7q?p=preview

Answer 3

Maybe you could use the Object.keys function?

var users = {
  "Jack": 24,
  "White": 25
};

var user_history = [
  "Jack",
  "White"
];

function add_user(name, data) {
  var keys = Object.keys(users);
  var first_user;

  if (keys.length > 10) {
    first_user = user_history.shift();
    delete users[first_user];
  }

  users[name] = data;
  user_history.push(name);
}

add_user("Steven");

More info about Object.keys here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/keys

Answer 4

First, if you know your limit is 10, just use the loop.

First and halfth: constructors should begin with capital letter ;-) You write the code for people that will read it, not for the machine (machine is ok with 0s and 1s).

Second, for these use cases (when n can be higher), to get decent performance you need to use two structures at the same time: queue (implemented for example as array) to be able to add / remove items from it; and key-value store (object in JS, Map in upcoming ES6). To access via key you then use the kvs, to add/remove you use the queue while updating the kvs at the same time.

If you are interested in fast queue implementing, you may look up "Circular queue" or use some lib (eg. https://github.com/herby/queue).