Brief JavaScript Reference TBE 540 Start End JavaScript script Language JavaScript functions etc script Functions little programs Functions are small program that are called started by some event like clicking a button or an image A function can also be called from another function The parentheses are always used after the function name Sometimes a value or a variable is placed inside the parentheses to pass it on to another function function nameOfFunction instructions here Examples of calling a function input type button value Send Number onClick sendOne Num img src BIG gif onClick goThere if X 7 small Variables var variableName var variableName initial value If the variable is declared outside any functions it is global works in all functions If the variable is declared inside a function it is local only works in that function ALERT and PROMPT Boxes These commands are used to display information on the screen ALERT boxes show a message PROMPT boxes show a message and wait for input Examples ALERT HI THERE PROMPT What is your name X Note The after the comma allow you to put in a default value FORMs buttons boxes menus FORMs are another way to display information and get input Instead of floating on top of the page like ALERT they are part of the page The most commonly used FORM elements are buttons and text boxes Example makes a CLICK HERE button and a place for a name that will hold 20 characters FORM input type button value CLICK HERE onClick sendName CLICK HERE input type text size 20 name username FORM There are other types of FORM elements that might be useful Radio buttons are small round buttons while checkboxes are square Both are used to get input usually from a list of choices Radio buttons are generally set up so that the user can only choose one They are good for multiple choice tests Checkboxes are usually used when the user can make more than one choice Examples assuming there was a FORM tag somewhere above the command INPUT type checkbox name Favorite Food value Big Mac Big Mac INPUT type radio name Favorite Color value Rainbow Rainbow Some web pages use pull down menus like this SELECT name Favorite Computer OPTION SELECTED Mac OPTION IBM OPTION Apple II SELECT Menus are also useful for multiple choice tests or surveys The code looks like this Textareas are larger boxes for text An example 5 rows 30 columns TEXTAREA name message rows 5 cols 30 TEXTAREA Loops Repetitions Loops repeat a series of commands a given number of times for loops or until a given condition is true while loops Loops use a variable that is a counter keeps track of how many times the loop has repeated Braces are used to show which commands are repeated Examples for var j 0 j 10 j Use variable j as a counter start at 0 j 0 keep going while j is less than 10 j 10 add 1 to j each repetition j repeated statements while var k 140 Use variable k add 1 to k each repetition k keep going while K is less than 140 repeated statements IF Statements decisions Statements containing if are used when you want the program to make a decision based on a condition often whether a variable is equal to a set value There are several possibilities 1 If the condition is true perform a set of instructions otherwise go to the next instruction 2 If the condition is true perform a set of instructions otherwise perform a different set of instructions Braces are used to show which instructions should be done Note means exactly equal to Examples if Age 50 alert YOU ARE OLD If the value of the variable Age is greater than 50 display YOU ARE OLD If not just go to the next line If Ans TRUE If the variable Ans is equal to the word TRUE alert RIGHT display RIGHT else otherwise alert WRONG display WRONG Calculations Calculations use these symbols add subtract multiply divide power A calculation usually begins with a variable name var X 100 testScore There are also shortcuts such as var p means add 1 to this variable Random Numbers Random numbers use built in Math functions For example the code get a random number from 0 to 10 is Math floor Math random 11 Math random gives a decimal number between 0 and 0 999999 Multiplying it by 11 gives a decimal number from 0 to 10 999999 Math floor eliminates the decimal part making it a whole number between 0 and 10 If you want to round to the nearest whole number use Math round