class102-06.md

Dynamic Web Pages with JavaScript

Resources:

• JavaScript
• Input Output in plain JavaScript
• JavaScript Variables

Overview

JavaScript is a lightweight compiled programming language with first class functions (functions are treated like any other variable). It is primarily used as a scripting language for web pages, but is also used in non-browser environments as well.

Javascript Variables

Variables are containers for storing values and there are three (3) ways to declare them in JavaScript.

1. var
2. let
3. const

    <p id="demo"></p>
    <script>
        var x = 5;
        var y = 6;
        var z = x + y;
        document.getElementById("demo").innerHTML =
        "The value of z is: " + z;
    </script>

Identifiers

All JavaScript variables must be identified with unique names (aka identifiers).

General Rules for Identifiers:

• length can be one (1) digit or longer
• must begin with a letter, $, OR _
  • $ is often used as an alias for the main function in a JavaScript library
  • _ is often used for private or hidden variables
• may contain letters, numbers, $, OR _
• are case sensitive (x and X are considered different)
• cannot be JavaScript keywords

Assignment Operator

The equal sign = is an assignment operator in JavaScript, and not considered equal to (denoted as ==)

Data Types

• strings: written in "double" or 'single' quotes
• numbers: written without quotes

Declaring Variables

Declaring a variable, creates a variable, and can be done with the var keyword. When intially created a variable has no assigned value. To assign a value use the assignment operator = either in the same line of text as the variable creation, or afterwards on a separate line.

var Name;
Name = "Erik";

OR

var Name = "Erik";

Both set name = to "Erik".

Additional Points:

• You can declare multiple variables in one statement.
• Variables declared without a value will be undefined.

Arithmetic

• use +, = to do simple arithmetic