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Apache Cordova- storing Data through Apps

Anonymous User 2074 17-Apr-2017

In the series of learning apache Cordova framework using node.js, this article is another step in forward direction that explains the ways to store data in an app.

Also Read: Introduction to Apache Cordova

You can use storage APIs that are available for storing data on the client apps. This will be helpful for the app when the user is offline and also for improving performance of the app. You will be able to know how to store data in an app, also you will learn about the plugins you can use, in our next article posts.

So, here are the steps, for how can you store data:

Step 1 - Adding Buttons

You will have to create four buttons in index.html file. The buttons must be placed inside div class = "app" element.

<button id = "setLocalStorage">SET LOCAL STORAGE</button>
 


<button id = "showLocalStorage">SHOW LOCAL STORAGE</button>

<button id = "removeProjectFromLocalStorage">REMOVE PROJECT</button

<button id = "getLocalStorageByKey">GET BY KEY</button>Local Storage Buttons


Apache Cordova- storing Data through Apps

Step 2 - Adding Event Listeners

You have to add event listeners inside the index.js files as Cordova’s security policy doesn't allow inline events. We will also assign window.localStorage to a localStorage variable that we will use later.

document.getElementById("setLocalStorage").addEventListener("click", setLocalStorage);


document.getElementById("showLocalStorage").addEventListener("click", showLocalStorage);

document.getElementById("removeProjectFromLocalStorage").addEventListener

   ("click", removeProjectFromLocalStorage);

document.getElementById("getLocalStorageByKey").addEventListener

   ("click", getLocalStorageByKey);

 

var localStorage = window.localStorage;       

 Step 3 - Creating Functions

Now, you will need to create the functions that will be called when the buttons are tapped upon. First function is used for adding data to local storage.

function setLocalStorage() {


   localStorage.setItem("Name", "John");

   localStorage.setItem("Job", "Developer");

   localStorage.setItem("Project", "Cordova Project");

}

 The next one will log data we added to console.

function showLocalStorage() {


   console.log(localStorage.getItem("Name"));

   console.log(localStorage.getItem("Job"));

   console.log(localStorage.getItem("Project"));

}   

 

If we tap SET LOCAL STORAGE button, we will set three items to local storage.

If we tap SHOW LOCAL STORAGE afterwards, the console will log items that we want.

John

Index.js:70

Developer

Index.js:71

Cordova Project

Index.js:72

 

Now let's create function that will delete the project from the local storage.

function removeProjectFromLocalStorage() {


   localStorage.removeItem("Project");

}

 If we click SHOW LOCAL STORAGE button after we deleted the project, the output will show null value for the project field.

John

index.js:70

Developer

index.js:71

null

index.js:72

 

We can also get the local storage elements by using key() method which will take the index as an argument and return the element with corresponding index value.

function getLocalStorageByKey() {


   console.log(localStorage.key(0));

}

 

Now when we tap the GET BY KEY button we will get the following output.

Job
Index.js:83

 

NOTE:

When we use key() method, the console will log job in place of name even though we passed argument 0 to fetch first object. This is happening as data stored in local storage in alphabetical order.

The following table shows all local storage methods available.

S N

Methods & Details

1

setItem(key, value)

 

Used for setting the item to local storage

 

2

getItem(key)

 

Used for getting the item from local storage.

 

3

removeItem(key)

 

Used for removing the item from local storage.

 

4

length()

 

Used for retreiving the number of items that exists in local storage.

 

5

clear()

 

Used for removing all the key/value pairs from local storage.

 

6

key(index)

 

Used for getting the item by using the index of the item in local storage. Items are sorted alphabetically

 

You may also like: How to install Apache Cordova


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