Terms:

pragmatic design

A little of both. Planning will help get the job done in a more organized fashion. Trying out detail tasks in small programs will ensure that you can in fact accomplish the end goal.

functions as problem solvers

functions that give answers. Functions that give answers do so by returning a value. The value can be used in any JS expression. Examples of functions you have used that return a value:

var x = window.prompt("enter value", "1"); // value is text string the user enters
var y = document.getElementById("someID").value; // value is a property of some element
if ( isNaN(x) ) x = 0;  // value is true or false

predefined functions

Javascript has many pre-defined functions for us to use including Math functions such as square root and rounding numbers.

Practical Example

	var textAmt = document.getElementById("liters").value;;
	var liters = parseFloat(textAmt); // now it is a number
	var rounded = Math.round(liters*10)/10; // now its rounded to 1 decimal places

There are numerous Math functions. Some of the more frequently used are:

	Math.floor (3.7);  // return the integer below 3.7 (i.e., 3)
	Math.ceil (4.2);  // return the integer above 4.2 (i.e., 5)
	Math.round (3.7);  // round the integer 3.7 (i.e., 4)
	Math.sqrt (25);  // calculate square root
	Math.min (x, y);  // return the smallest of x and y
	Math.max (x, y);  // return the largest of x and y

Math functions can be called from within Javascript code as:
	1 + Math.sqrt(4)
	alert(Math.sqrt(4));

• We generally place our javascript functions in the HEAD section of html
• functions just perform a sequence of tasks

Daily Chores Finish all homework Clean room Put away laundry

Weekly Chores Cut the grass Put out the trash Put away video games

• Each has a unique name: we don't want to get the shopping list confused with a list of chores.
• In programming we use this kind of function to
• Make the code look neater and more readable
• Test the code once and re-use it many times
• Make the code easier to maintain
• Try it

<script language = 'JavaScript'> var shots = 1; var drink = "none"; var ounce = 0; </script> <input type = button value = "Clear" onClick = 'shots = 1; drink = "none"; ounce = 0; document.Bean.price.value = "0.00"'>

<script > var shots = 1; var drink = "none"; var ounce = 0; </script> function clearSettings() { shots = 1; drink = "none"; ounce = 0; document.Bean.price.value = "0.00" } <input type = button value = "Clear" onClick = 'clearSettings()'>

1. Let's create a function from our previous example of converting pounds to kilograms
2. Next, add html and a function to convert feet to meters (1 foot = 0.3048 meters

• Math.random generates a pseudo-random number in the range [0…1)
• pseudo-random refers to the fact that the numbers appear randomly distributed, but are in fact generated by a complex algorithm
  this function has no inputs; it returns a different number each call
  Math.random() -> 0.33008525626748814
  Math.random() -> 0.213335955823927
  Math.random() -> 0.8975001737758223
• a call to Math.random can be placed in an expression to affect the range
  2*Math.random() -> [0…2)
  Math.random() + 1 -> [1…2)
  9*Math.random() + 1 -> [1…10)
  Math.floor(9*Math.random() + 1) -> 1, 2, 3, …, 9

• setInterval function used to repeatedly execute a Javascript statement
  • setInterval('myFunction()', 5000)
  • First parameter is code to run or function to call
  • Second parameter is the frequency at which the first parameter is run in milliseconds
  • 5 milliseconds is 5 seconds
  • Every 5 seconds myFunction() is called
• setTimeout function is the time that a Javascript statement is executed
  • setTimeout('myFunction()', 5000)
  • First parameter is code to run or function to call
  • Second parameter is how long before the first parameter is run in milliseconds
  • 5 milliseconds is 5 seconds
  • In 5 seconds myFunction() is called