LocalStorage and JSON.stringify JSON.parse

Question

I have been working on a project that allows the user to submit memories about a place they have visited and tracks the location of when the memory was submitted. My only problem is trying to use localStorage with the app, I read about the JSON.stringify and JSON.parse, and don't understand how to use them in my code yet.

This is my form.js It processes the form and grabs the text fields. It clears the form when the add button(on the display details page) or the enter details button is clicked. Finally it receives the information and sends out the message back to the window.

function processForm(){

var locate = document.myform.locate.value;
var details = document.myform.details.value;
var storeData = []; 
localStorage.setItem("locate", JSON.stringify(locate));
localStorage.setItem("details", JSON.stringify(details));
alert("Saved: " + localStorage.getItem("locate") + ", and " + localStorage.getItem("details"));

var date = new Date,
    day = date.getDate(),
    month = date.getMonth() + 1,
    year = date.getFullYear(),
    hour = date.getHours(),
    minute = date.getMinutes(),
    ampm = hour > 12 ? "PM" : "AM";    
    hour = hour % 12;
    hour = hour ? hour : 12; // zero = 12
    minute = minute > 9 ? minute : "0" + minute;
    hour = hour > 9 ? hour : "0" + hour;

    date = month + "/" + day + "/" + year + " " + hour + ":" + minute +  " " + ampm;

localStorage.setItem("date", JSON.stringify(date));

storeData.push(locate, details, date);
localStorage.setItem("storeData", JSON.stringify(storeData));   
}

function clearForm(){
$('#myform').get(0).reset();
}

function retrieveFormInfo(){

var data = JSON.parse(localStorage.getItem("storeData"));   

var locate = JSON.parse(localStorage.getItem("locate"));
$("#locate2").html("Place: " + locate);

var details = JSON.parse(localStorage.getItem("details"));
$("#details2").html("Description: " + details);

var date = JSON.parse(localStorage.getItem("date"));
$("#date").html(date);

}

But the major problem I am running into is I do know how to take that information in correctly using the JSON.stringify and JSON.parse and appending it to the window with html elements dynamically, Mainly like a list of memories.

Any help is appreciated!

Post the relevant code here next time - see http://www.sscce.org/ for some ideas how to create a useful sample from your code. You've already setup an array once in your code - `storeData = []`, and added elements to it - `storeData.push()`. What you're probably looking to do though, is use an object, because you'd want to give a name to each value you're adding - e.g. date, hour, minute. You can do that by creating an object - `store = {}`, and then adding properties to it - `store['date'] = ...`. — Sacho, May 19 '14 at 02:15

gp. · Answer 1 · 2022-03-31T13:35:56.317

localStorage stores key value pairs as strings only (you can use integer for keys but they get converted to string automatically).

Storage objects are simple key-value stores, similar to objects, but they stay intact through page loads. The keys and the values are always strings (note that, as with objects, integer keys will be automatically converted to strings) reference

let's say you have an array to be stored with each item being a json object.

You got 2 options:

Option 1:

stringify every item and store in locaStorage

var item = {input1: 'input1value', input2: 'input2value' };
localStorage.setItem( itemIndex, JSON.stringify(item) );

to retrive the items iterate over localStorage items and then convert the item to JSON object:

for(var i=0;i<localStorage.length; i++) {
  var key = localStorage.key( i );
  var item = JSON.parse( localStorage.getItem( key ) );
}

Option 2:

stringify the entire array and store in localStorage

localStorage.setItem( 'memoriesdata', JSON.stringify( arr ) );

to read the data read the item as string then convert to JSON object
```
var arr = JSON.parse( localStorage.getItem('memoriesdata') );
```

*"(keys can also be integers)"* No, keys are strings. If you use an integer (or boolean, or anything else) as the key, it will be converted to string. — T.J. Crowder, Mar 31 '22 at 08:09
@T.J.Crowder you are right. looks like the reference page text got updated. I updated the text in my answer as well to avoid any confusion. — gp., Mar 31 '22 at 13:36

sabithpocker · Answer 2 · 2014-05-19T02:31:38.803

First get values of your input fields into a javascript object.

var myMemory = {};
myMemory.location = document.getElementById('location').value;
myMemory.description = document.getElementById('description').value;

Now save myMemory to localStorage,this can be done on a form submission or a button press. We can store as an array of memories and add item to it every time.

//if user already has memories in local, get that array and push into it.
//else create a blank array and add the memory.
memories = localStorage.getItem('memories') ?
              JSON.parse(localStorage.getItem('memories')) : 
              [];
memories.push(myMemory);
localStorage.setItem('memories', JSON.stringify(memories));

public override · Answer 3 · 2014-05-19T04:45:19.643

I use this Storage implementation. It's inspired by many storage plugins out there... It handles any value serilizable by JSON.stringify function, and should work xbrowser (and in 'cookie-disabled' firefox):

//
//    api:
//
// .clear()    empties storage
// .each()     loops storage (key, value) pairs
// .fetch()    get a value by key
// .has()      checks if there is a key set
// .ls()       lists all keys 
// .raw()      string value actually stored
// .reload()   reads in serialized data
// .rm()       removes key(s)
// .set()      setup value(s)
// .type()     storage type used 'localStorage/globalStorage/userData'
// .valid()    is storage engine setup correctly
//
;
((function(name, def, glob, doc) {

  // add 'store' id to globals
  this[name] = def(glob, doc);
}).call(
  this, "store", function(glob, doc) {

    // private (function) store version
    var stclient;

    var driver = {
      // obj  : storage_native{},
      // type : storage_type
    };

    var engine = {
      // read  : (func),
      // write : (func)
    };

    var _ = {

      a: Array.prototype,
      del: function(node) { // , ...fields

        _.slc(arguments, 1).
        forEach(function(field) {
          delete this[field];
        }, node);

        return node;
      },
      each: function(array, callback, context) {

        context ||
          (context = array);

        array.
        some(function() {
          return false === callback.apply(context, arguments);
        });

        return array;
      },
      hasown: Function.prototype.call.bind(Object.prototype.hasOwnProperty),
      jsdc: JSON.parse, // decode
      jsec: JSON.stringify, // encode 
      keys: Object.keys, // shimed .keys
      ns: "storage5", // single property name to keep serialized storage data under
      object: null, // parsed storage data 
      slc: Function.prototype.call.bind(Array.prototype.slice),
      test: {

        isemptyobj: function(node) {
          for (var x in node)
            return false;
          return true;
        },

        isplainobj: function(node) {
          return '[object Object]' == Object.prototype.toString.call(node);
        },

      },
      testval: 'storage' + Math.random(), // test value for implementation check
      rig: function(target, items) {

        for (var field in items)
          if (items.hasOwnProperty(field))
            target[field] = items[field];

        return target;
      },
      clone: function(node) {
        return _.jsdc(_.jsec(node));
      },
      puts: function() {
        engine.write(_.jsec(_.object));
      },
    };

    stclient = function storage5() {
      return arguments.length ?
        storage5.set.apply(storage5, arguments) :
        storage5.fetch();
    };

    // _init on load|ready
    window.addEventListener('load', _init, false);

    return _.rig(stclient, {

      clear: function() {
        return _.object = {}, _.puts(), this;
      },

      each: function(callback, context) {

        context ||
          (context = this.fetch());

        _.each(this.ls(), function(field) {
          return callback.call(context, field, this.fetch(field));
        }, this);

        return this;
      },

      fetch: function(key) {
        return (arguments.length) ?
          _.object[key] : _.clone(_.object);
      },

      has: function(name) {
        return _.hasown(_.object, name);
      },

      ls: function() {
        return _.keys(_.object);
      },

      raw: function() {
        return engine.read();
      },

      reload: _load,

      rm: function() {

        _.del.apply(null, _.a.concat.apply([_.object], arguments));

        return _.puts(), this;
      },

      set: function(input, value) {

        var len = arguments.length;
        var flag = 1;

        if (len) {

          if (_.test.isplainobj(input)) {

            _.keys(input).
            forEach(function(field) {
              _.object[field] = input[field];
            });

          } else {

            if (1 < len)
              _.object[input] = value;
            else
              flag = 0;

          }

          flag && _.puts();

        }

        return this;
      },

      type: function() {
        return driver.type || null;
      },

      valid: function() {
        return !_.test.isemptyobj(driver);
      },

    });

    function _init() {

      var flag = 0;
      var stnative;

      if ("localStorage" in glob) {
        try {
          if ((stnative = glob["localStorage"])) {
            // inits localStorage 
            _initlocst(stnative, driver, engine);
            flag = 1;
          }
        } catch (e) {}
      }

      if (!flag) {

        if ("globalStorage" in glob) {
          try {
            if ((stnative = glob["globalStorage"])) {
              // inits globalStorage
              _initglobst(stnative, driver, engine);
              flag = 1;
            }
          } catch (e) {}
        }

        if (!flag) {
          // inits userDataStorage
          _initusrdatast(doc.createElement(_.ns), driver, engine);
        }
      }

      // parse serialized storage data
      _load();
    }

    function _initlocst(stnative, driver, engine) {

      stnative[_.testval] = _.testval;

      if (_.testval === stnative[_.testval]) {

        try {
          stnative.removeItem(_.testval);
        } catch (e) {
          try {
            delete stnative[_.testval];
          } catch (e) {}
        }

        driver.obj = stnative;
        driver.type = "localStorage";

        engine.read = function() {
          return driver.obj[_.ns];
        };

        engine.write = function(stringvalue) {
          driver.obj[_.ns] = stringvalue;
          return stringvalue;
        };

      }
    }

    function _initglobst(stnative, driver, engine) {

      var host = glob.location.hostname;

      driver.obj = (/localhost/i).test(host) ?
        stnative["localhost.localdomain"] : stnative[host];

      driver.type = "globalStorage";

      engine.read = function() {
        return driver.obj[_.ns];
      };

      engine.write = function(stringvalue) {
        driver.obj[_.ns] = stringvalue;
        return stringvalue;
      };

    }

    function _initusrdatast(node, driver, engine) {

      try {

        node.id = _.ns;
        node.style.display = "none";
        node.style.behavior = "url('#default#userData')";

        doc.
        getElementsByTagName("head")[0].
        appendChild(node);

        node.load(_.ns);

        node.setAttribute(_.testval, _.testval);
        node.save(_.ns);

        if (_.testval === node.getAttribute(_.testval)) {

          try {

            node.removeAttribute(_.testval);
            node.save(_.ns);

          } catch (e) {}

          driver.obj = node;
          driver.type = "userData";

          engine.read = function() {
            return driver.obj.getAttribute(_.ns);
          };

          engine.write = function(stringvalue) {
            driver.obj.setAttribute(_.ns, stringvalue);
            driver.obj.save(_.ns);
            return stringvalue;
          };

        }

      } catch (e) {
        doc.
        getElementsByTagName("head")[0].
        removeChild(node);
      }

      node = null;
    }

    function _load() {

      try {
        _.object = _.jsdc((engine.read() || engine.write("{}")));
      } catch (e) {
        _.object = {};
      }
    }

  }, window, document));

  //eof

score 2 · Accepted Answer · edited Nov 20 '20 at 06:59

Vanilla JS:

var printStorageBody = function () {
    var body = document.querySelector("body");
    var pre = document.createElement("pre");
    body.innerHTML = "";
    pre.innerText = JSON.stringify(localStorage, null, '\t');
    body.appendChild(pre);
}

jQuery:

var printStorageBody = function () {
    $("body").html("");
    $("<pre>")
    .text(JSON.stringify(localStorage, null, '\t'))
    .appendTo("body");
}

LocalStorage and JSON.stringify JSON.parse

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