JavaScript

JavaScript

1. OUTPUT

   • window.alert()
     • Alert box
   • document.getElementById(id)
     • innerHTML- gets content
     • id attribute in HTML- defines
   • console.log()
     • Use for debugging
   • document.write()
     • Dangerous!
     • Only use when testing

2. Begin by using <script> tags at the end of <body> in HTML

   • Improves display speed
   • Can src a .js file inside <script>
     • External .js file good if use is for multiple webpages

3. ARRAYS

   • Indexing is 0 based
     • colors[1] =blue
   • Arrays are objects
     • var colors = [ 'red', 'blue', 'green'];

4. FUNCTIONS

   • Task executed when called
     • Stops at return statement
   • function name(p1, p2) { return task }
     • vars defined inside are local

5. METHODS

   • A property whos value is a function
     • Helps working with different datatypes
     • pop(), push(), length(), concat(), toString(), indexOf(), getDate()

6. DATATYPES & VARIABLES

   • Datatypes: undefined, null, boolean, string, number, object
     • typeof- finds datatype
   • Declare variables: var, let, const
     • Assign variables: =
     • No assignment = undefined
   • var number = 27;
     • Can perform mathematics
   • var string = "word";
     • "" = ' '
     • Can concatenate together
   • var person = {Name : 'Jack'}
   • Setting a value to null has type object
   • booleans =true/false

7. OBJECTS

   • Variable with many values
   • var face = { eyeColor: 'blue' , shape: 'oval'}
     • Named values are Properties
       • access using obName.propName
     • Functions stored as properties are Methods
       • access using obName.methName( )
       • this -refers to object

8. EVENTS

   • HTML event attributes with JS
   • <element event='JS'>
     • eg. <button onclick= 'JS'>
   • Often call functions