Extra 16-1  Develop a Contact List app that uses JSON

Extra 16-1 Develop a Contact List app that uses JSON

Extra 16-1  Develop a Contact List app that uses JSON

In this exercise, you'll develop a Contact List application that uses the JSON object to convert objects to strings and back again for storage in local storage. The application looks like this:


And this is the JSON string that's stored in local [email protected]"}]


1.       Open the HTML and JavaScript files

2.       Review the code in the contact_list.js file. Note that it uses a storage object and Contact objects to add and display contacts.

3.       In the library_storage.js file, add code to the getContacts method that converts a string to a JavaScript object and returns it, or returns an empty array if the string is null.

4.       Still in the library_storage.js file, add code to the setContacts method that converts a JavaScript object to a string.

5.       In the library_contact.js file, review the code for the Contact constructor function and its methods. Then, add code to the toJSON method that shortens the property names (you can refer to the JSON string above to see what the short names should be).

6.       Still in the library_contact.js file, add code to the loadJsonObject method that uses the object with short names to populate the Contact object's properties.

7.       Run and test the application. Notice that it allows you to store a phone number with dashes, slashes, plus signs, etc., but it displays the phone numbers exactly as you enter them.





body {

  font-family: Verdana, Arial, Helvetica, sans-serif;

  font-size: 100%;

  background-color: white;

  width: 800px;

  margin: 0 auto;

  border: 3px solid blue;

  padding: 0 2em 1em;


h1 { 

  font-size: 150%;

  color: blue;

  margin-bottom: .5em;


label {

  float: left;

  width: 8em;


input {

  width: 22em;

  margin-right: 1em;

  margin-bottom: 1em;


input[type="button"] {

  width: 10.5em;


.clear {

  clear: both;


#contacts {

  width: 50%;

  margin: 0 3em 0 0;

  float: right;




"use strict";

var $ = function (id) { return document.getElementById(id); };

var contacts = [];


var displayContacts = function () {

  // clear previous

  contacts.length = 0;

  $("contacts").innerHTML = "";


  // get contacts from storage and initialize a variable to hold html string

  var array = storage.getContacts();

  var html = "";


  // loop array from storage, create new Contact objects, store

  // them in contacts array and use the displayContact method for display

  for (var i = 0; i < array.length; i++) {

    var contact = new Contact();


    html = html.concat("<tr<td", contact.displayContact(),"</td</tr");

    contacts[i] = contact;



  // display html string and set focus on first textbox

  $("contacts").innerHTML = html;




var addContact = function () {  

  // get values from textboxes

  var first = $("first").value;

  var last = $("last").value;

  var org = $("org").value;

  var phone = $("phone").value;

  var email = $("email").value;


  // use values to add new Contact object

  var contact = new Contact(first, last, org, phone, email);


  // contact is valid, 

  if (contact.isValid()){

    // add contact to array and reset local storage




    // clear text boxes and re-display contacts



  } else {  

    alert("Please enter a first and last name, and a phone number or email address.");





var clearTextBoxes = function() {

  $("first").value = "";

  $("last").value = "";

  $("org").value = "";

  $("phone").value = "";

  $("email").value = "";



var eraseContacts = function() {


  contacts.length = 0;

  $("contacts").innerHTML = "";




window.onload = function() {

  $("add_contact").onclick = addContact; 

  $("erase").onclick = eraseContacts;





<!DOCTYPE html



  <titleContact List</title

  <link type="text/css" rel="stylesheet" href="contact_list.css"

  <script type="text/javascript" src="library_storage.js"</script

  <script type="text/javascript" src="library_contact.js"</script

  <script type="text/javascript" src="contact_list.js"</script




  <h1My Contacts</h1

  <table id="contacts"</table


  <label for="first"First Name:</label<br

  <input type="text" name="first" id="first"<br

  <label for="last"Last Name:</label<br

  <input type="text" name="last" id="last"<br

  <label for="org"Organization:</label<br

  <input type="text" name="org" id="org"<br

  <label for="phone"Phone:</label<br

  <input type="text" name="phone" id="phone"<br

  <label for="email"Email:</label<br

  <input type="text" name="email" id="email"<br


  <input type="button" name="add_contact" id="add_contact" value="Add Contact"

  <input type="button" name="erase" id="erase" value="Erase Contacts"

  <div class="clear"</div






"use strict";


var Contact = function(first, last, org, phone, email) {

  if (arguments.length 0) {

    this.firstName = first;

    this.lastName = last;

    this.organization = org;

    this.phone = phone;

    this.email = email;




Contact.prototype.isValid = function() {

  // must have first and last name, and either phone number or email address

  var isValid = true; 

  if (this.firstName === "" || this.lastName === "") { isValid = false; }

  if (this.phone === "" && this.email === "") { isValid = false; }

  return isValid;



Contact.prototype.displayContact = function() {

  return this.firstName.concat(" ", this.lastName, ", ", 

    this.organization, "<brPhone: ", this.phone, " <brEmail: ",

    this.email, "<hr");



Contact.prototype.loadJsonObject = function(obj) {

  // use json object from storage to populate properties




Contact.prototype.toJSON = function() {

  // shorten property names for storage





"use strict";


var storage = {

  keyContacts: "contacts_1",

  getContacts: function() {    

    // get string from local storage 

    var storageString = localStorage.getItem(this.keyContacts) || null;


    // convert string to JavaScript object and return, or return empty array if string is null



  setContacts: function(value) {

    // convert JavaScript object to string  


    // store string in local storage  

    localStorage.setItem(this.keyContacts, storageString);


  clearContacts: function() {

    localStorage.setItem(this.keyContacts, "");


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