JavaScript LocalStorage

JavaScript LocalStorage; Through this tutorial, i am going to show you javascript localStorage & types of methods in localStorage with the help of examples.

JavaScript localStorage

  • What is LocalStorage?
  • Types of Methods in JavaScript localStorage
  • localStorage with condition statement Loop
  • Example for Build a todo app with JavaScript LocalStorage
  • Advantage and Disadvantage of localStorage
  • FAQ’s JavaScript localStroage

What is LocalStorage in JavaScript?

In JavaScript, localStorage is a type of web storage that allows storing data locally within the user’s browser with no expiration date for javascript sites and apps. This data will not be deleted when the browser is closed and will be available when the browser is opened again.

Types of Methods in JavaScript localStorage

There are six basic JavaScript localStorage methods to use localStorage in your web applications for access and work with localStorage:

  1. setItem(): Add key and value to localStorage
  2. getItem(): Retrieve a value by the key from localStorage
  3. removeItem(): Remove an item by key from localStorage
  4. clear(): Clear all localStorage
  5. key(): Passed a number to retrieve nth key of a localStorage
  6. length – the number of stored items.

localStorage setItem

localStorage setItem() method allows us to store data locally in key-value pairs within the user’s browser.

The following syntax represents the setItem() method:

localStorage.setItem(key, 'Value');

Here,

  • The key means by which name the data will be stored locally.
  • Value means what value you will store in the associate key.

Note that localStorage can only store strings.

localStorage getItem

localStorage getItem() method allows to fetch data using a particular key within the user’s browser

The following syntax represents the getItem() method:

 localStorage.getItem('key') 

Here,

  • The name of the key you want to retrieve the value of.

localStorage removeItem

localStorage removeItem() method allows to remove data using a particular key within the user’s browser

The following syntax represents the removeItem() method:

 localStorage.removeItem('key') 

Here,

  • The name of the key you want to delete the value of.

localStorage clear

localStorage clear() method allows to clear or delete all local storage data within the user’s browser

The following syntax represents the clear() method:

 localStorage.clear() 

localStorage key

localStorage key() method allows to passing a number or index to localStorage to retrieve the name of the key.

The following syntax represents the key() method:

localStorage.key(index);

localStorage length

localStorage length method allows to get the presence of items stored locally in the within the user’s browser:

The following syntax represents the length method:

localStorage.length

localStorage with Condition statement and Loop

To check some items in localStorage, you can use javascript length() method with if else statement. See the following example:

if (localStorage.length > 0) {
  // We have items
} else {
  // No items
}

To iterate localStorage data, you can use javascript for loop. The following example represents how to iterate localStorage items with for loop:

for (let i = 0; i < localStorage.length; i++){
  let key = localStorage.key(i);
  let value = localStorage.getItem(key);
  console.log(key, value);
}

Example for Build a todo app with JavaScript LocalStorage

Use the following instruction to create todo app using javascript localStorage with HTML 5.

First of all, create a simple HTML front end with index.html. And loading in the bootstrap library and style.css for styling to-do app.

Index.html

<!DOCTYPE html>
<html>
  <head>
    <link
      rel="stylesheet"
      href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta.3/css/bootstrap.min.css"
      integrity="sha384-Zug+QiDoJOrZ5t4lssLdxGhVrurbmBWopoEl+M6BdEfwnCJZtKxi1KgxUyJq13dy"
      crossorigin="anonymous"
    />
    <link rel="stylesheet" type="text/css" href="src/styles.css" />
  </head>
  <body>
    <div
      class="body-overlay opacity-80"
      style="background-color: #151c54"
    ></div>
    <div class="container">
      <div class="header">
        <h1>TO DO LIST</h1>
      </div>
      <div class="input-group mb-3">
        <input
          type="text"
          class="form-control taskname"
          placeholder="Enter Your Task"
          aria-label="Recipient's username"
          aria-describedby="basic-addon2"
        />
        <div class="input-group-append">
          <button type="button" class="btn btn-primary btnTask">
            Add Task
          </button>
        </div>
      </div>
      <ul class="tasklist"></ul>
      <button type="button" class="btn btn-link btnClear">Clear All</button>
    </div>
    <script src="src/index.js"></script>
  </body>
</html>

Remember that, create one folder name scr and as well as create two files first one is style.css and second one is scritp.js inside scr folder.

Update the following CSS into your src/style.css file:

h1,
p {
  text-align: center;
}
body {
  color: #435757;
  background-image: url(https://learnwith.hasinhayder.com/wp/wp-content/uploads/2018/07/emile-perron-190221-unsplash-banner.jpg);
  background-color: linear-gradient(-20deg, #d0b782 20%, #a0cecf 80%);
  font-family: Roboto, sans-serif;
  height: 100vh;
  background-size: cover;
  background-repeat: no-repeat;
  background-position: center center;
}
.container {
  max-width: 570px;
  top: 125px;
  margin: 0 auto;
  padding: 12px 25px 50px;
  border-top: 5px solid rgba(255, 255, 255, 0.16);
  background: linear-gradient(
    to right,
    #0dabf31c 0,
    #2b2f5c00 51%,
    #2a2e5b00 100%
  );
  background-color: rgba(22, 27, 72, 0.83);
  user-select: none;
  z-index: 100;
  position: relative;
  box-shadow: 0 10px 15px 2px rgba(0, 0, 0, 0.1);
}
.body-overlay {
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  opacity: 0.79;
  z-index: 10;
}
ul {
  padding: 0;
}
.header {
  padding-bottom: 17px;
}
p {
  font-size: 15px;
  color: #0dabf3;
  top: -42px;
  margin-top: -13px;
  font-family: cursive;
}
.list-group-item {
  padding: 0.75rem 1.25rem;
  border-bottom: 1px dashed rgba(169, 167, 167, 0.34) !important;
  border: none;
  color: #fff;
  font-size: 19px;
  font-weight: 300;
}
.btnTask {
  background: #0dabf3;
  margin-left: 5px;
}
.list-group,
.list-group-item {
  background: 0 0 !important;
}
.btnClear,
.btnClear:hover {
  color: #ffc107;
  float: right;
}
h1 {
  margin: 0;
  padding: 20px;
  color: #0dabf3;
}

Here’s what it looks like after updating css into your file.

Set up some variables for the web page elements like the form, the unordered list, the button, and the text input.

var inp = document.querySelector(".taskname");
var list = document.querySelector(".tasklist");
var addTask = document.querySelector(".btnTask");
var taskClear = document.querySelector(".btnClear");
var taskList = [];

Next, Make a function that creates an li element on the web page.

function render(elemments) {
  list.innerHTML = "";
  elemments.forEach(e => {
    let newEl = document.createElement("li");
    newEl.innerHTML = e;
    newEl.classList.add("list-group-item");
    list.appendChild(newEl);
  });
}

Add event listener to the form that watches for a click event, which will be any time you click add task button on the form. 

Call the render() function, which will create the item with the text of the input value and append it to the DOM using js push() method. Finally, we’ll set the input value to an empty string so you don’t have to erase the last item entered manually.

addTask.addEventListener("click", e => {
  if (inp.value !== "") {
    taskList.push(inp.value);
    inp.value = "";
    render(taskList);
    taskClear.style.display = "block";
    localStorage.setItem("mylist", JSON.stringify(taskList));
  } else {
    alert("Please input your task");
  }
});

Our taskList is being reset to an empty array every time the script runs. We could fix this by making a conditional statement that checks if localStorage already exists, such as in the below example.

let saved = localStorage.getItem("mylist");
if (saved) {
  taskList = JSON.parse(localStorage.getItem("mylist"));
  render(taskList);
} else {
  taskClear.style.display = "none";
}

Last, we’ll add a click event to the button that will clear all data from localStorage, as well as removing every child node from the ul.

taskClear.addEventListener("click", function() {
  localStorage.clear();
  list.innerHTML = "";
  taskList = [];
  taskClear.style.display = "none";
});

Update the javascript code into your scr/script.js file:

var inp = document.querySelector(".taskname");
var list = document.querySelector(".tasklist");
var addTask = document.querySelector(".btnTask");
var taskClear = document.querySelector(".btnClear");
var taskList = [];
function render(elemments) {
  list.innerHTML = "";
  elemments.forEach(e => {
    let newEl = document.createElement("li");
    newEl.innerHTML = e;
    newEl.classList.add("list-group-item");
    list.appendChild(newEl);
  });
}
addTask.addEventListener("click", e => {
  if (inp.value !== "") {
    taskList.push(inp.value);
    inp.value = "";
    render(taskList);
    taskClear.style.display = "block";
    localStorage.setItem("mylist", JSON.stringify(taskList));
  } else {
    alert("Please input your task");
  }
});
let saved = localStorage.getItem("mylist");
if (saved) {
  taskList = JSON.parse(localStorage.getItem("mylist"));
  render(taskList);
} else {
  taskClear.style.display = "none";
}
taskClear.addEventListener("click", function() {
  localStorage.clear();
  list.innerHTML = "";
  taskList = [];
  taskClear.style.display = "none";
});

Advantage and Disadvantage of localStorage

See the advantage and disadvantage of localStorage; as shown below:

Advantages of localStorage

  • It stores up to 5-10MB of data (depending on the browser).
  • Easy to use – no need for a web server or backend database.
  • Great for getting an idea up and running and for testing purposes.

Disadvantages of localStorage

  • It only stores up to 10MB of data (5MB in some browsers).
  • It can only store strings. This can restrict you from using it for more complex scenarios; although, HTML can be stored as a string – more on that later…
  • It’s local to the browser and specific to the origin (per domain and protocol), and there’s no guarantee that the data will persist even in that same context.

FAQ’s JavaScript localStroage

Here, i will provide you some faqs about javaScript localhstroage; as shown below:

1: How to get data from localstorage in javascript?

You can use localStroage.setItem() method.

2: How to remove or delete data from localStorage data in javascript?

You can use localStorage.getItem() method.

3: How to remove or delete data from localStorage data in javascript?

You can use localStorage.removeItem() method.

4: How to clear all localStorage data in javascript?

You can use localStorage.clear() method.

You can see the all localStorage method below, asked in the given question.

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