What is JavaScript?

• JavaScript (often shortened to JS) is a cross-platform programming language for Web pages.
• The JavaScript standard is ECMAScript.
• All modern browsers fully support ECMAScript 5.1

JavaScript values

• JavaScript recognizes the five following types of primitive values:

JavaScript Variables

• You use variables as symbolic names for values in your application.
• You can declare a variable in this way:
  • With the keyword "var". For example,

    var x = 42;

  • A variable declared using the var statement with no initial value specified has the value undefined.

    var x;
    console.log(x); // undefined

JavaScript Operators

• JavaScript has both binary and unary operators, and one special ternary operator, the conditional operator.
• A binary operator requires two operands, one before the operator and one after the operator:

  x * y;

• A unary operator requires a single operand, either before or after the operator:

  x++;

Comparison operators

JavaScript functions

• A function definition consists of the "function" keyword, followed by
  • the name of the function
  • a list of arguments to the function, enclosed in parentheses and separated by commas
  • the JavaScript statements that define the function, enclosed in curly braces, "{ }".

JavaScript function example

function square(number) {
  return number * number;
}

function sum(x, y) {
  return x + y;
}

Calling functions

• Defining a function does not execute it.
• Calling the function actually performs the specified actions with the indicated parameters.
• For example, if you define the function square, you could call it as follows:

  square(5);

What is jQuery?

• jQuery is a cross-platform JavaScript library designed to simplify the client-side scripting of HTML
• jQuery is the most popular JavaScript library in use today.

Including the library

• The jQuery library is a single JavaScript file
• It is possible to include jQuery directly from content delivery networks:

  <script src="http://code.jquery.com/jquery-1.11.min.js">

Usage style

• You can use jQuery via the "$"" function.
• Examples:

  $('body').append('ciao2');
  
  $('body').html('ciao');
  
  $('img').attr('src', 'image.jpg')
  

jQuery Ajax

• The jQuery library has a full suite of Ajax capabilities.
• The functions and methods allow us to load data from the server without a browser page refresh.

jQuery Ajax example

$.ajax({
  url: "test.html"
}).done(function(content) {
  $('body').html(content);
});