How to Save and Restore a File Object in Local Storage

How do I save and restore a File object in local storage

You cannot serialize file API object.

Not that it helps with the specific problem, but ...
Although I haven't used this, if you look at the article it seems that there are ways (although not supported yet by most browsers) to store the offline image data to some files so as to restore them afterward when the user is online (and not to use localStorage)

save restore local storage to a local file

The process for saving and retrieving local storage has two parts.

First you must be able to retrieve the contents of local storage in a form that is manageable in javascript. Since local storage is a map of key-value pairs the easiest way to this is to turn local storage into a javascript object. Then take this object and turn it into a JSON string. What you do with this string is up to you but I find it easiest to just have the user copy the string into an email.

function getLocalStorage() {
    var a = {};
    for (var i = 0; i < localStorage.length; i++) {
        var k = localStorage.key(i);
        var v = localStorage.getItem(k);
        a[k] = v;
    }
    var s = JSON.stringify(a);
    return s;
}

When I get the string, I use the following function to turn my local storage into a copy of their local storage. Remember to wipe your local storage clean before duplicating their data with a call to localStorage.clear()

function writeLocalStorage(data) {
    var o = JSON.parse(data);
    for (var property in o) {
        if (o.hasOwnProperty(property)) {
            localStorage.setItem(property, o[property]);
        }
    }
}

The last part of your question is how to protect the data from overwriting. You can't write to a local file, however, you can have copy the data into <textarea> and tell the user how to copy and paste the data into a email or a more direct approach.

Storing Objects in localStorage

local storage limited to handle only string key/value pairs you can do like below using JSON.stringify and while getting value JSON.parse

var testObject ={name:"test", time:"Date 2017-02-03T08:38:04.449Z"};

Put the object into storage:

localStorage.setItem('testObject', JSON.stringify(testObject));

Retrieve the object from storage:

var retrievedObject = localStorage.getItem('testObject');

console.log('retrievedObject: ', JSON.parse(retrievedObject));

How to store objects in HTML5 localStorage/sessionStorage

Looking at the Apple, Mozilla and Mozilla again documentation, the functionality seems to be limited to handle only string key/value pairs.

A workaround can be to stringify your object before storing it, and later parse it when you retrieve it:

var testObject = { 'one': 1, 'two': 2, 'three': 3 };

// Put the object into storage
localStorage.setItem('testObject', JSON.stringify(testObject));

// Retrieve the object from storage
var retrievedObject = localStorage.getItem('testObject');

console.log('retrievedObject: ', JSON.parse(retrievedObject));

Save image file in local storage and retrieve image from file path html angularjs

For storing and retrieving image from local storage you can simply use javascript. Here is an example:

    bannerImage = document.getElementById('bannerImg');
    imgData = getBase64Image(bannerImage);
    localStorage.setItem("imgData", imgData);

    function getBase64Image(img) {
        var canvas = document.createElement("canvas");
        canvas.width = img.width;
        canvas.height = img.height;

        var ctx = canvas.getContext("2d");
        ctx.drawImage(img, 0, 0);

        var dataURL = canvas.toDataURL("image/png");

        return dataURL.replace(/^data:image\/(png|jpg);base64,/, "");
}

Here is the link to the StackOverflow question

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