What is the best way to create a collection of key-value pairs in JavaScript that allows for efficient value retrieval and iteration in a specific order?

Looking for a way to store key/value pairs in a JavaScript object? Say you have orange=123, banana=4, apple=567. How can you achieve the following:

  1. Retrieve a value using a specific key, like set["orange"] should yield 123.
  2. Iterate over the set in the order the values were added.

An object literal is suitable for point 1 but may not guarantee the iteration order. On the other hand, an array of key/value pairs (object literals) could ensure the desired iteration order but might lack keyword lookup functionality.

@* Thanks for all the help - Is this a common issue? Do libraries like jQuery offer solutions for these scenarios?

Answer №1

Ever thought about creating your own custom list constructor?

function CustomList(obj) {

  if (this instanceof CustomList) {
   var instance = this,
       keysArray = [];

    /* Initialize: add the properties of [obj] to the list, 
       and store the keys of [obj] in the private keys array */
    for (var prop in obj) {
       keysArray.push(prop);
       instance[prop] = obj[prop];
    }
    /* Public:
       Add a property to the list 
    */
     instance.add = 
         function(key, value) {
              instance[key] = value;
              keysArray.push(key);
              return instance; /* Allows method chaining */
            };

    /* Public:
       Return raw or sorted list as a string, separated by [separator] 
       Without [sort], the order of properties is maintained based on 
       the order in which they were added to the list
    */
     instance.iterate =
       function(sort, separator){
         separator = separator || '\n';
         var resultArr   = [],
             sortedKeys = sort ? keysArray.slice().sort() : keysArray;

         for (var i = 0; i < sortedKeys.length; i++){
           resultArr.push(sortedKeys[i] + ': ' + instance[sortedKeys[i]]);
         }
       return resultArr.join(separator);
      };

  } else if (obj && obj instanceof Object) {
     return new CustomList(obj);

  } else if (arguments.length === 2) { 
     var newObj = {};
     newObj[String(arguments[0])] = arguments[1];
     return new CustomList(newObj);

  } else { return true; }

 /* The 'if (this instanceof List)' pattern makes
    the use of the 'new' operator unnecessary. The 
    constructor also allows initialization with
    2 parameters => 'CustomList(key,value)' 
 */
}

You can now view the raw list (maintains the order properties were added) or a sorted list:

var myList = 
 CustomList( { orange:123,
              banana:4,
              apple:567 }
          );
myList.add('peach',786);
alert(myList.iterate());
  /*=>output:
    orange: 123
    banana: 4
    apple: 567
    peach: 786
  */
or: alert(myList.iterate(1));
  /*=>output:
    apple: 567
    banana: 4
    orange: 123
    peach: 786
  */

Answer №2

Both of your observations are accurate. Object literals do not guarantee a specific order for keys.

To address this issue without creating a custom data structure, one option is to maintain a predefined list of keys:

var obj = {
    orange: 123,
    banana: 4,
    apple: 567
}

var keys = ['orange', 'banana', 'apple'];

for (var i = 0; i < keys.length; i++){
  value = obj[keys[i]];
}

Although not the most elegant solution, it gets the job done.

Answer №3

An example of a neat encapsulation:

class Dictionary {
    constructor(initialData) {
        this.keys = [];

        if (initialData !== undefined) {
            this.Add(initialData);
        }
    }

    Add(dataToAdd) {
        if (!Array.isArray(dataToAdd)) { dataToAdd = [dataToAdd]; }

        for (let i = 0; i < dataToAdd.length; i++) {
            for (let key in dataToAdd[i]) {
                this[key] = dataToAdd[i][key];
                this.keys.push(key);
            }
        }
    }
}

const myDictionary = new Dictionary({ 'orange': 123, 'banana': 4, 'apple': 567 });

alert(myDictionary.keys); // returns [orange, banana, apple]

alert(myDictionary.keys[0]); // returns orange

alert(myDictionary.orange); // returns 123

myDictionary.Add({ 'mango': 88 }); // adding data another way

myDictionary.Add([{ kiwi: 16 }, { grapefruit: 79 }]); // adding data yet another way

alert(myDictionary.keys); // returns [orange, banana, apple, mango, kiwi, grapefruit]

Answer №4

There are several ways to accomplish this task:

let x = {'blue':567, 'red':890, 'green':432};

let y = new Object();
y['blue'] = 567;
y['red'] = 890;
y['green'] = 432;

let z = new Object();
z.blue = 567;
z.red = 890;
z.green = 432;

Although the syntax varies, all three declarations have the same internal functionality.

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