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JavaScript – return function, time object and image rollover

JavaScript – return function, time object and image rollover. Function that provides a return. We seen function eg. displayText() We seen function with parameters function f1(varName) eg. markBox(cell)

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JavaScript – return function, time object and image rollover

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  1. JavaScript – return function, time object and image rollover

  2. Function that provides a return • We seen function eg. displayText() • We seen function with parameters function f1(varName) eg. markBox(cell) • Today we tackle function that returns something. It could return a number, a string, a boolean or even an “object” • Might need it for TIC TAC TOE assignment – especially for checkWin()

  3. Example: function calcArea(l, w) {/* function calculates and returns */ var area = l*w; return area; } function calcPerim(l, w) { return (2 * l * w); //a short cut without using temp var } function calc() { var wid=parseFloat(document.simpleForm.widthBox.value); var len=parseFloat(document.simpleForm.lengthBox.value); calcArea(len, wid); calcPerim(len, wid); document.simpleForm.showArea.value = area; document.simpleForm.showPerim.value = perimeter; }

  4. Example of function return function calcArea(l, w) {/* function calculates and returns */ var area = l*w; return area; } function calcPerim(l, w) { return (2 * l * w); //a short cut without using temp var } function calc() { var wid=parseFloat(document.simpleForm.widthBox.value); var len=parseFloat(document.simpleForm.lengthBox.value); var area = calcArea(len, wid); // call a fn with parameters var perimeter = calcPerim(len, wid); document.simpleForm.showArea.value = area; document.simpleForm.showPerim.value = perimeter; }

  5. Exercise: Displaying Time. • For this exercise, you need to be able to use the previous jex12.html to help you. You DO NOT need random function. • The only part is how to create current time. • There is a Date object. Use the code here below to create a timeStamp variable that is of object type Date(). See the code below in order to get the hrs, mins and seconds. var timeStamp = new Date(); hrs = timeStamp.getHours(); mins = timeStamp.getMinutes(); seconds = timeStamp.getSeconds(); • Note that hrs, mins and seconds are declared as numeric integer. In order to print them in HH:MM:SS, you need to concatenate into string ie. displayString = hrs + ":" + mins + ":" + seconds;

  6. Exercise: Displaying Time. displayString = hrs + ":" + mins + ":" + seconds; • Then you write the following code to display the time. document.simpleForm.displayTime.value = displayString; • However, if any of hrs, mins or seconds are less than 10, then the time might look wierd, eg. • 9:4:5 which actually suppose to mean 09:04:05 • Therefore you need to write some if conditions to include a "0" in front. • displayString can be concatenated to itself. For example if displayString shows "bc" and you want to make it "abc", you do displayString= "a" + displayString; • displayString shows "bc" and you want to make it "bcd", you do displayString = displayString + "d";

  7. Exercise jex14.html: From trial to reality • First try and get the seconds out of the time stamp and see if you can animate the seconds moving and stopping. • Once this works, then you try and get the whole time to display correctly. Do not worry about the 09 vs. 9 minutes at this point. Once you are able to display the time, then you start to write the if condition to check. • Once this works, then you can use style sheet to modify your textbox. Look at POP/TART exercise

  8. Image Roll Over • You have seen this applications of image roll over in many web pages especially for menu choices etc. • The two event handlers that deals with image roll over are • onmouseover • This is when the mouse is on top of the image • onmouseout • This is for handling the event when the mouse leaves the image. • You need to preload all the images into arrays in order to facilitate this feature.

  9. Example – in body of HTML <BODY> <A href="links.html" onmouseover = "change(0)" onmouseout = "changeback(0)"> <img src="links1.gif" width=97 height=26 border=0 align=bottom></A> <A href="pics.html" onmouseover = "change(1)“ onmouseout = "changeback(1)"> <img src="pics1.gif" width=97 height=26 border=0 align=bottom ></A> <A href="demos.html" onmouseover = "change(2)" onmouseout = "changeback(2)"> <img src="demos1.gif" width=97 height=26 border=0 align=bottom ></A> </BODY>

  10. Example – JavaScript code var roll_in = new Array(); var roll_out = new Array(); for(i=0; i<3; i++) { roll_in[i]=new Image(); roll_out[i]= new Image(); } roll_in[0].src="links1.gif"; roll_in[1].src="pics1.gif"; roll_in[2].src="demos1.gif"; roll_out[0].src="links2.gif"; roll_out[1].src="pics2.gif"; roll_out[2].src="demos2.gif"; function change(whichOne) { document.images[whichOne].src = roll_out[whichOne].src; } function changeback(whichOne) { document.images[whichOne].src=roll_in [whichOne].src; } Be careful here. You may have to adjust the “index” of the images. Sometimes it will be whichOne + x where x is the number of displayed images prior to the roll over images

  11. Exercise jex15.html – Web page with image roll over.

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