Saving Javascript Module Object in local storage

Question

i have a javascript module name SceneModule, see the code snippet below

var SceneModule = function()    {
    var scene, createScene, updateScene, getScene;

    scene   =   {
        name : '',
        width : 100,
        height : 100
    };

    createScene = function(params)  {
        for(var key in params)  {
            scene[key] = params[key];
        }

        return this;
    };

    updateScene = function(params)  {
        scene[params.attr] = params.value;
    };

    getScene = function()   {
        return scene;
    }

    return {
        create : function(params)   {
            createScene(params);
        },

        update : function(params)   {
            updateScene(params);
        },

        get : function()    {
            getScene();
        }
    };
};

var SceneArray = [], tempArray;

SceneArray.push(
    SceneModule.create({
        name : 'scene 1',
        width : 100,
        height : 100
    }),
    SceneModule.create({
        name : 'scene 2',
        width : 100,
        height : 100
    }),
    SceneModule.create({
        name : 'scene 3',
        width : 100,
        height : 100
    })
);

localStorage.setItem('scene',JSON.stringify(SceneArray);

tempArray = JSON.parse(localStorage.getItem('scene'));

/**
 * Print string [object object, object object, object object];
 * not the SceneArray Structure; 
 */
console.log(tempArray);

When I put the array of object to local storage and retrieve it, I get a string ([object object, object object, object object]) not the object array itself. I am also new to the modular architecture and local storage. I tried what many levels that i know to store and get the array of object. please review the code block. thanks in advance

Raynos · Accepted Answer · 2012-01-27 07:36:32Z

No. You cannot store functions or closures in localStorage. This means that you cannot store state stored in closures explicitly in localStorage.

Your current code actually prints [null, null, null] because it's broken.

After fixing your code it correctly prings [{}, {}, {}] because you only have methods

Mainly because JSON doesn't support functions. There are two solutions

Use a real prototypical OO module

Live Example - Here I'm using pd-style prototypical OO

var Scene = { 
    /* insert methods */   
};

var SceneArray = [], tempArray;

SceneArray.push(
    extend(Object.create(Scene), {
        name : 'scene 1',
        width : 100,
        height : 100
    }),
    extend(Object.create(Scene), {
        name : 'scene 2',
        width : 100,
        height : 100
    }),
    extend(Object.create(Scene), {
        name : 'scene 3',
        width : 100,
        height : 100
    })
);

localStorage.setItem('scene', JSON.stringify(SceneArray));

tempArray = JSON.parse(localStorage.getItem('scene')).map(function (data) {
    return extend(Object.create(Scene), data);
});
console.log(tempArray); // [Object, Object, Object]

Here only methods go on the Scene prototype and you extend your object that inherits from Scene with the actual data. You store the actual data in localStorage and when you take it out of local storage you map them to objects that inherit from Scene to get your methods back.

Implement a save and load function

Live Example - The trick here is to save the data and then pack the data into a SceneModule object.

// unpack the data and only save the data
localStorage.setItem('scene', JSON.stringify(SceneArray.map(function (scene) {
    return scene.get();
})));

// pack the data back into a scene module.
var tempArray = JSON.parse(localStorage.getItem('scene')).map(function (data) {
    return SceneModule().create(data);
});

Note that unlike the prototypical OO example you have to unpack your objects in the save stage. Prototypical OO has the advantage of your objects just being your state and because only the properties own data are it's own properties it's completely safe to just save the object without modification.

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Saving Javascript Module Object in local storage

1 Answer 1

Use a real prototypical OO module

Implement a save and load function

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Collectives™ on Stack Overflow

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Use a real prototypical OO module

Implement a save and load function

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