Loading JSON Data

This project shows you how to load JSON data in two ways. First, from an asset in the project. Second, over HTTP from a remote server.

Loading JSON from an asset

Game.attributes.add('characterData', {
    type: 'asset',
    assetType: 'json'
});

//...

Game.prototype.parseCharacterData = function (data) {
    var names = [];

    // Read the character data from the JSON asset return a list of names
    var characters = data.characters;
    for (var i = 0; i < characters.length; i++) {
        var character = characters[i];
        names.push(character.firstName + ' ' + character.lastName);
    }

    return names;
};

//...

// Get JSON data from a project asset
var characterData = this.characterData.resource;

// Parse JSON data
var names = this.parseCharacterData(characterData);

You can see in the code above that all you need to do to load JSON data from an asset in your project is to use a Script Attribute of type 'asset' or to retrieve the asset from the asset registry, then access the resource property. For an asset of type json the data will already be parsed into a standard javascript object when you access the resource property.

Once you have the javascript object you can access the data as normal. For example, looping through properties as in parseCharacterData.

Loading JSON from a remote server

Game.prototype.loadJsonFromRemote = function (url, callback) {
    var xhr = new XMLHttpRequest();
    xhr.addEventListener("load", function () {
        callback(JSON.parse(this.response));
    });
    xhr.open("GET", url);
    xhr.send();
};

//...

// load JSON from a remote server
this.loadJsonFromRemote("https://api.github.com/", function (data) {
    // display JSON data from remote server
    el = document.querySelector("#xhr-json");
    el.textContent = JSON.stringify(data, null, 4);
});

In this code we are using the XMLHttpRequest object (which is part of the standard web browser API) to request JSON data from a URL, in this case the Github API.

After receiving the "load" event we parse the JSON data using JSON.parse (another part of the standard web browser API) and return the data via the callback function.

Note, that the call to loadJsonFromRemote is asynchronous.

Here is the full code listing:

var Game = pc.createScript('game');

Game.attributes.add('display', {
    type: 'asset',
    assetType: 'html'
});

Game.attributes.add('style', {
    type: 'asset',
    assetType: 'css'
});

// Create a script attribute to enable the drag and drop of a JSON asset containing character data
Game.attributes.add('characterData', {
    type: 'asset',
    assetType: 'json'
});

// initialize code called once per entity
Game.prototype.initialize = function() {
    this.initDisplay();

    var el;

    // Get JSON data from a project asset
    var characterData = this.characterData.resource;

    // Parse JSON data
    var names = this.parseCharacterData(characterData);

    // display character names
    el = document.querySelector("#character-name");
    el.textContent = names.join(", ");

    // display JSON data from asset
    el = document.querySelector("#asset-json");
    el.textContent = JSON.stringify(characterData, null, 4);

    // load JSON from a remote server
    this.loadJsonFromRemote("https://api.github.com/", function (data) {
        // display JSON data from remote server
        el = document.querySelector("#xhr-json");
        el.textContent = JSON.stringify(data, null, 4);
    });
};

Game.prototype.initDisplay = function () {
    var el = pc.createStyle(this.style.resource);
    document.head.appendChild(el);

    var div = document.createElement("div");
    div.setAttribute("id", "container");
    div.innerHTML = this.display.resource;
    document.body.appendChild(div);
};

Game.prototype.parseCharacterData = function (data) {
    var names = [];

    // Read the character data from the JSON asset return a list of names
    var characters = data.characters;
    for (var i = 0; i < characters.length; i++) {
        var character = characters[i];
        names.push(character.firstName + ' ' + character.lastName);
    }

    return names;
};

Game.prototype.loadJsonFromRemote = function (url, callback) {
    var xhr = new XMLHttpRequest();
    xhr.addEventListener("load", function () {
        callback(JSON.parse(this.response));
    });
    xhr.open("GET", url);
    xhr.send();
};

Try the project for yourself.