VARIABLES, COMMENTS, FUNCTIONS

• Single line comment


  Starts with a //
• Multi-line comment


  Starts with /* and ends with */
• Variable


  A value that can change, depending on the conditions or on the information passed on to the program
• Keywords for variable declaration

  • var
  • let
  • const
  • None
• When to use var


  • If you want your code to run in older browsers
  • It is used in all javascript code from 1995 to 2015
• When to use let

  • Variables defined with let cannot be redeclared
  • It must be declared before use
  • It has a block scope
• When to use const

  • Variables defines with const cannot be redeclared
  • It cannot be reassigned
  • It has a block scope
• Variable naming rules


  • Names can contain letters, digits, underscores, and dollar signs
  • Names must begin with a letter
  • Names can also begin with $ and _
  • Names are case sensitive
  • Reserved words cannot be used as names
• Function


  A block of code designed to perform a particular task

  Defined with the function keyword, followed by a name, followed by a parentheses
• Parameters


  Listed inside the parentheses () in the function definition
• Arguments


  The values received by the function when it is invoked
• Function invocation


  • When an event occurs
  • When it is invoked (called) from JavaScript code
  • Automatically (self-invoked)
• Return keyword


  • Function open compute return value
  • The returned value is returned back to the caller
• Why use functions


  • To reuse the code
  • To avoid repetition of codes
  • To use the same code with different arguments for different outcomes