nested hashtables in javascript

Question

I want to create the following data-structure with js:

folders dictionary: folder-id(guid) : ==> pages dictionary

pages array: page-position(int) : ==> files dictionary

files dictionary: file-id(guid) : ==> file object

I want to know at each time how many items are in each collection.

How would you suggest me to implemet this in JS ?

Should I use array or object with dynamically added properties?

Are the keys all primitives? I.e., can all keys be converted into strings correctly? — pimvdb
– pimvdb, Commented Feb 17, 2012 at 20:03
@pimvdb I was asking because his question looked like he didn't, and if he didn't I would have explain it in an answer. — Incognito
– Incognito, Commented Feb 17, 2012 at 21:59

Oybek · Accepted Answer · 2012-02-17 20:21:54Z

2

Do the classes as follows.

function HashTable() {
    var content = {};
    var count = 0;
    this.Add = function(key, value) {
        if (content.hasOwnProperty(key)) throw new Error("Key already exist");
        content[key] = value;
        count++;
    };
    this.Set = function(key, value) {
        if (!content.hasOwnProperty(key)) count++;
          content[key] = value;
    };
    this.Get = function(key) {
        if (!content.hasOwnProperty(key)) throw new Error("No such key");
        return content[key];
    };
    this.AllKeys = function() {
        var keys = [];
        for (a in content) {
            keys.push(a);
        }
        return keys;
    };
    this.Count = function() {
        return count;
    };
    this.Remove = function(key) {
        if (!content.hasOwnProperty(key)) throw new Error("No such key");
        delete content[key];
        count--;
    };
}


// Then you can use it as follows

var folders = new HashTable();
folders.Add(1, 10);
alert(folders.Count());
alert(folders.Get(1));
folders.Remove(1);
alert(folders.Count());

It gives you a more rigid and OOP approach.

Edit

This ensures that your keys are unique, gives you count at any time and accepts integers and strings as keys.

answered Feb 17, 2012 at 20:21

Oybek

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2 Comments

Elad Benda Over a year ago

How can I use and write this ctor not in the global scope?

Oybek Over a year ago

@EladBenda Put the definition in the global scope. Then you can instantiate it anywhere.

phihag · Accepted Answer · 2012-02-17 20:16:20Z

2

You can just write it out:

var folders = {
    'folder1-guid': [
        {'file1-guid': 'file1-content'},
        {'file2-guid': 'file1-content'}
    ]
};

Alternatively, create Object and Array instances and assign the properties to them.

answered Feb 17, 2012 at 20:16

phihag

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3 Comments

pimvdb Over a year ago

+1 And "how many items" could be done using Object.keys(obj).length.

Elad Benda Over a year ago

Should I use array or object with dynamically added properties?

phihag Over a year ago

Use an array if you want to express a (potentially ordered) set of elements, and an object if you want to have a mapping of strings to elements.

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