JavaScript Cheat Sheet

• Variables:
  • Variables are containers for storing data values.
• Arithmetic: + - * / %
  • % is for modulo. Modulo returns the remainder after integer division. For example 17 % 7 results in 3 since 17 divided by 7 has a remainder of 3.
• Math Functions:
  • Math.PI
  • Math.round()
    • Math.round( x ) returns the value of x rounded to its nearest integer.
    • Math.ceil( x ) returns the value of x rounded up to the nearest integer.
    • Math.floor( x ) returns the value of x rounded down to the nearest integer.
  • Math.pow()
    • Math.pow( x, y ) returns the value of x to the power of y.
  • Math.sqrt()
    • Math.sqrt( x ) returns the square root of x.
  • Math.random()
    • Returns a random number between 0 (inclusive), and 1 (exclusive).
• Types and Type Casting: number, string, boolean
  • typeof( x )
    • Returns the type name of x as a string.
  • Number( x )
    • A function that converts strings to numbers.
    • Number( "3" ) returns 3
    • Number( "John" ) returns NaN (Not A Number)
  • String( x )
    • Converts the value of x into a string.
    • String( 45 ) converts the number 45 into the string "45"
    • String( true ) converts the boolean true into the string "true"
• Strings:
  • +
    • Concatenates two strings (puts them together into one string)
    • Example: "Go " + "Navy" evaluates to "Go Navy"
  • x.length
    • Returns the length of string x.
    • 'Hello'.length returns 5
  • x.charAt( y )
    • Returns the character at position y in string x.
    • Indexing starts at 0.
    • 'Hello'.charAt( 1 ) returns "e"
  • x.charCodeAt( y )
    • Returns the ASCII decimal value of the character at position y in string x.
    • "Hello".charCodeAt( 1 ) returns 101
  • String.fromCharCode( x )
    • Returns a string consisting of the ASCII character represented by the decimal value x.
• Input and Output:
  • alert( x ) (Output)
    • Displays a popup window with the value of x.
    • E.g. alert("Hello World!");
      Produces a popup window that says Hello World!
  • prompt( x ) (Input)
    • Produces a popup window with the value of x with a text box for the user to enter a value.
    • Returns a string of what the user entered into the text box.