Mixing Index Array with "Associative Array"

Question

Since I need to access my items sometime by index and sometime by code. Is it a good idea to mix integer index with string index?

Note that the code, index, amount of items never changes after the data is loaded.

I'm thinking of doing something like this, where the same object is pushed and set as a hashtable.

function DataInformation(code, dataValue) {
    this.code = code;
    this.dataValue = dataValue;
}

var dataList = [];

function fillDataList() {
    addNewData(new DataInformation("C1", 111));
    addNewData(new DataInformation("C2", 222));
    addNewData(new DataInformation("C3", 333));
}

function addNewData(newData) {
    dataList.push(newData);
    dataList[newData.code] = newData;
}

Then I would be able to access the object with either:

dataList[0].dataValue
dataList["C1"].dataValue

Before I used to loop to find the item.

function findItemByCode(code) {
    for (var i = 0; i < dataList.length; i++) {
        if (dataList[i].code == code) {
            return dataList[i];
        }
    }

    return null;
}

findItemByCode("C1").dataValue

JavaScript does not have associative arrays. It has arrays and it has objects. — gen_Eric
– gen_Eric, Commented Aug 8, 2016 at 14:45
It is an interesting idea, to have both, one to sort, and one for quick indexing. And since object are passed by reference. A change in a property of the objects in a table, will reflect in the other. — Mic
– Mic, Commented Aug 8, 2016 at 15:00

Tomalak · Accepted Answer · 2016-08-08 14:50:39Z

3

Do you ever need to iterate dataList in strict order? Or is it just a bag of items for which you want random access by a certain key?

If ordered iteration is not a concern, use an object instead of an array. Watch out for key clashes, though.

var dataList = {};

function addNewData(newData) {
    dataList[newData.code] = newData;
    dataList[newData.dataValue] = newData;
}

// that's it, no other changes necessary

If key clashes can occur - or ordered iteration is necessary, or if you just want to make it particularly clean, use an array and an accompanying index object.

var dataList = [];
var dataIndex = {
    byCode: {},
    byValue: {}
};

function addNewData(newData) {
    dataList.push(newData);
    dataIndex.byCode[newData.code] = newData;
    dataIndex.byValue[newData.dataValue] = newData;
}

answered Aug 8, 2016 at 14:50

Tomalak

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1 Comment

the_lotus Over a year ago

All keys are different. You gave me good ideas here, I'll do something like this (with better naming). var dataIndex = { byCode: {}, dataList: [] };

Vladu Ionut · Accepted Answer · 2016-08-08 15:10:44Z

Here is my try using Proxies

// Code goes here

function DataInformation(code, dataValue) {
  this.code = code;
  this.dataValue = dataValue;
}

var _dataList = [];
var dataList = new Proxy(_dataList, {
  get: function(target, name) {
    if (target && target.myMap && target.myMap[name]) return target[target.myMap[name]];
    return target[name];
  },
  set: function(obj, prop, value) {
    // The default behavior to store the value
    obj.myMap = obj.myMap || {};
    obj.myMap[value.code] = prop;
    obj[prop] = value;
    return true;
  }
});

function fillDataList() {
  addNewData(new DataInformation("C1", 111));
  addNewData(new DataInformation("C2", 222));
  addNewData(new DataInformation("C3", 333));
}

function addNewData(newData) {
  dataList.push(newData);
}

fillDataList();

console.log(dataList[0].dataValue);
console.log(dataList["C1"].dataValue);

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