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JavaScript - Objects, Functions And Drawing (newbie Question)
Hi Everyone
I am trying to write some code to create an object in JS that contains the x,y coords for a shape i wish to draw. I create the shape, and then in a draw function I draw the shape to the screen from the object I created erlier. Trouble it is does not seem to work :S have anyone got and ideas? Code: var myShape = new newShape(200,200);
function init() {
canvas = document.getElementById("canvas");
ctx = canvas.getContext("2d");
return setInterval(draw, 50);
} // init
function newShape(x,y){
this.un_X=x
this.un_Y=y
function drawAll() {
ctx.beginPath();
ctx.arc(un_X,un_Y,30,0,Math.PI*2,true);
ctx.closePath();
ctx.stroke();
} // drawAll
} // newShape
function draw() {
ctx.clearRect(0, 0, WIDTH, HEIGHT);
myShape.drawAll();
} // draw
init();
Thanks in advance Similar Tutorialshi. i know a little php, but new to javascript. much of the syntax is identical. i'm reading the new rhino book (flanagan 6th). in it, where he introduces METHODS, he says "When we combine FUNCTIONS with OBJECTS we get METHODS". Then he creates an empty ARRAY: Code: var a = []; then he uses the "push() method" to add elements to the array. Code: a.push(1,2,3); uh, methods are for *objects* right? Yet he is using them on an ARRAY. Can somebody help me see the light on how an array can magically becomes an object that is manipulated by a "method"? I mean, the array is still an array, no? It never actually becomes an object, right? Yet we still use a *method* to manipulate it. See my conceptual quandry? hi. i know a little php, but new to javascript. much of the syntax is identical. in reading the new rhino book (flanagan 6th), he gives the following example: Code: var square = function(x) {
return x*x;
};
okay, but then he does this: Code: square(plus1(y)) as an example of "invoking two functions in one expresson". (Prior he gives an example of defining a function with plus1, which is how I normally think of functions.) uh, square is a *variable*, but he is using it as a FUNCTION. Can somebody help me understand how this can be? how it works? I'm having trouble conceptualizng how we use a variable as a function. I'm having a spot of trouble in making my functions work and my book seems to be pure rubbish. I'm sure that the error is purely syntax, although it may be something more. Code: <script type="text/javascript" src="flowers.js"></script>
<script type="text/javascript">
function pageSetup() {
var today = new Date(); // this creates a date object with today's date
var banner = displayBanner(today); // *should* call the displayBanner function
var days = calcDaysToSale(today); // *should* call the function using today's date
document.sale.saleMessage.value = days; // *should* set the value to days.
// Obviously none of it works.
}
</script>
This is the code working with the script contained in the html file. I'll post the full page at the bottom. The following code is the JavaScript code. The first function isn't made to provide full functionality at the moment, I'm trying to get the rest of it working. Code: function displayBanner(currentDate) {
if (currentDate.getMonth() == 2)
imgSrc = "winterLogo";
return ("<img src='" + imgSrc + ".gif'>");
}
function calcDaysToSale(currentDate) {
var saleDay = new Date();
saleDay.setDate(15); // sets the sale date to the 15th of the current month
// Subtracts the days remaining until the sale.
// If the number is negative, the sale is over.
var Days = saleDay.getDate()-currentDate.getDate();
if (Days < 0) {
return "The sale has ended.";
}
else {
return Days;
}
}
I have tried to Google the problem and I have also tried to look it up in my book. I simply don't know the right terms to Google, and as I said the book is rubbish. I don't know why the Code: document.sale.saleMessage.value = days; doesn't work for this. Oh well, I'll learn quickly I suppose. Here is the full HTML code: Code: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Carol's Flowers</title>
<link href="flowers.css" rel="stylesheet" type="text/css" />
<script type="text/javascript" src="flowers.js"></script>
<script type="text/javascript">
function pageSetup() {
var today = new Date(); // this creates a date object with today's date
var banner = displayBanner(today); // *should* call the displayBanner function
var days = calcDaysToSale(today); // *should* call the function using today's date
document.sale.saleMessage.value = days; // *should* set the value to days.
// Obviously none of it works.
}
</script>
</head>
<body class="oneColLiqCtrHdr">
<div id="container">
<div id="header">
<p><img name="myBanner" src="banner" id="myBanner" alt="Carol's Flowers" />
<!-- end #header -->
</p>
<div id="links"><a href="#">Home</a> | <a href="#">General Arrangements</a> | <a href="#">Seasonal Designs</a> | <a href="#">Custom Orders</a> | <a href="#">Location</a></div>
</div>
<div id="mainContent">
<table id="mainTable">
<tr>
<td width="201"><h1><img src="Flowers.JPG" alt="Random Flowers" width="200" height="255" /></h1></td>
<td width="687">
<p>Here at Carol's Flowers, we believe that there is a perfect floral arrangment for every occasion! Take a look around and see if there is anything you like. If we don't already have it, then we will create it for you!</p></td>
</script>
</tr>
</table>
<!-- end #mainContent --></div>
<div id="footer">
<p> <form name="sale" id="sale">
Days Until Mid Month Madness Sale :
<input type="text" name="saleMessage" id="saleMessage" /></form></p>
<!-- end #footer --></div>
<!-- end #container --></div>
<!-- I am trying to run the script here -->
<script type="text/javascript">
pageSetup();
</script>
</body>
</html>
I have a javascript assignment I am having difficulties with. I have most of it complete but need some assistant with the last portion and that is to get my display function to work. I am sure that this is something I should know how to do but for the life of me can't seem to figure out and just need a little guidance. Code:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html lang="en" xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head>
<title>Lab03</title>
<h1> Person Information </h1>
<script type= "text/javascript" charset= "utf-8">
function Person( ) {
this.lastname = ' ';
this.firstname= ' ';
this.areacode= ' ';
this.phone_number= ' ';
this.show_person = ' ';
}
</script>
<script type= "text/javascript" charset= "utf-8">
var per1 = new Person
function getInput( ) {
lastname= prompt("please enter your last name: ");
firstname= prompt("please enter your first name: ");
areacode= prompt("please enter your area code: ");
phone_number= prompt ("Please enter your phone number (ex:888-8888): ");
return per1;
}
per1= getInput( );
</script>
</head>
<body>
<script type ="text/javascript" charset= "utf-8">
function show_person( ){
if( firstname == "" && lastname == "" )
{
document.writeln( "Name: Unknown" + "<br/>" );
}
else if( firstname == 'null' && lastname == 'null' )
{
document.writeln( "Name: Unknown" + "<br/>" );
}
else if ( firstname == "" || lastname == "")
{
document.writeln("Name: " + lastname);
document.writeln(firstname + "<br/>");
}
else if ( firstname == 'null' || lastname == 'null')
{
document.writeln("Name: " + lastname);
document.writeln(firstname + "<br/>");
}
else
{
document.writeln("Name: " + lastname + ", ");
document.writeln(firstname + "<br/>");
}
else if ( areacode == "" || phone_number == "" )
{
document.writeln ("Phone: ");
}
else if ( areacode == 'null' || phone_number == 'null' )
{
document.writeln ("Phone: ");
}
else
{
document.writeln('Phone: (' + areacode + ')');
document.writeln(phone_number);
}
return this.show;
}
</script>
<noscript>
<p>You must enable javascript to view all the features of this page.</p>
</noscript>
</body>
</html>
Can someone help me out and tell me what it is I need to do to make it work? I actually had it working when I was able to put all the code in the get function but was told I needed a separate display function so any input is greatly appreciated. This is a little hard to explain so I'm posting an example. Code: //NESTED FUNCTION I'M USING TO DEMONSTRATE MY QUESTION
function foo(a) {
this.x = 5;
//USED TO SET THE VALUE OF X
if( a == 0 )
return function(z) {
return x = z;
}
//USED TO RETRIEVE THE VALUE OF X
else if( a == 1 )
return function() {
return x;
}
}
//MAKES setX THE SETTER FUNCTION
var setX = foo(0);
//MAKES getX THE GETTER FUNCTION
var getX = foo(1);
print( "setX(25), not an instance: " + setX( 25 ) );
print( "getX(), not an instance: " + getX() );
print( "" );
//CREATES AN OBJECT INSTANCE USING FOO AS CONSTRUCTOR
var q = new foo();
print( "value of x in object instance: " + q.x );
print( "" );
print( "setX(25), not an instance: " + setX( 25 ) );
print( "getX(), not an instance: " + getX() );
This code will output: Code: setX(25), not an instance: 25 getX(), not an instance: 25 value of x in object instance: 5 setX(25), not an instance: 25 getX(), not an instance: 25 Observations: It seems like this.x actually has two meanings. 1)x becomes a member of the "Function" object foo(). 2)x becomes a part of the constructor for prototype class foo. But why then does x revert back to the original value of 5 when I use foo as a constructor? Does javascript automatically save the original value on creation for a reason? What is going on behind the scenes to make this happen? Is this behavior part of an ontological model that makes sense? Similarly, if I change "this.x" to "var x" I can access the value of x but I can't change it. Not that that I should be able to, the syntax "var x" doesn't make x a member of foo anyway. But I'm still having trouble classifying the relationship "var x" has to the function. Anyways this is more of a tangent. My main question is above but if anyone has something to say about this, I'd be interested to hear it. It seems like all these behaviors have rules to them, but there is no conceptual model to think through that guide these behaviors. Or maybe I'm just ignorant. Enlighten me. Hello, I'm taking Computer Logic in college. I only am truly familiar with HTML and CSS and minimal web hosting stuff. I REALLY want to learn how to program, however. Anyway, we are doing classes/objects and functions. I am trying to figure out how to do this exercise. She starts with having us make this page that has a form that lets you select one of three radio buttons that will change the background color of the web page, along with that there is two text boxes to put a first name and last name. Then there is a button to click which puts your full name concatenated in another box below. All of this, is done, and I pretty much THINK I understand what is going on. Here is the code that we did to get this to happen: Code: <html>
<head>
<title>Computer Logic in class</title>
<script type="text/javascript">
var nextColor = "";
var BR = "<br />";
function setColor(newColor)
{
nextColor = newColor;
}
function changeColor()
{
document.body.bgColor = nextColor;
}
function displayName()
{
var firstName = document.ColorAndText.firstName.value;
var lastName = document.ColorAndText.lastName.value;
document.ColorAndText.fullName.value = firstName + " " + lastName;
}
</script>
</head>
<body bgcolor="red">
<form name="ColorAndText" action = "">
<input type="radio" name="colors" value="Blue" onclick="setColor(this.value)"/> Blue <br />
<input type="radio" name="colors" value="LightYellow" onclick="setColor(this.value)"/> Light Yellow <br />
<input type="radio" name="colors" value="Yellow" onclick="setColor(this.value)"/> Yellow <br />
<input type="button" name="changeButton" value="changeColor" onclick="changeColor()" /> <br />
<input type="text" name="firstName" value="First Name" size="40" /><br />
<input type="text" name="lastName" value="Last Name" size="40" /><br />
<input type="text" name="fullName" readonly="true" size="40" /><br />
<input type="button" name="displayButton" value="Display name" onclick="displayName()" /> <br />
</form>
</body>
</html>
Okay, now, I have and can do that. Seems to make sense. Now, then, the actual program I need to make is from the following exercises: Activity 3-4 The owner of a flower shop wants you to develop a form for use on the shop's web site. The form should have a single text box for the user to enter his or her name. Under the text box should be a group of radio buttons for three different kinds of flowers: Roses, Carnations, and Daisies. Below the radio buttons should be a button labeled Request Info, with a read-only text box under it for thanking the user for requesting information. This program doesn't need any functions or onclick attributes for the graphical elements. Okay, here is the code that does that, very simple HTML. Code: <html>
<head>
<title>Computer Logic in class</title>
<script type="text/javascript">
var nextFlower = "";
var BR = "<br />";
function setFlower(newFlower)
{
nextFlower = newFlower;
}
function displayMessage()
{
var firstName = document.Flowers.nameBox.value;
document.Flowers.fullName.value = firstName + "," + nextFlower;
}
</script>
</head>
<body bgcolor="white">
<form name="Flowers" action = "">
<input type="text" name="nameBox" value="Namebox" size="60"><br />
<input type="radio" name="flowers" value="Roses" onclick="setFlower(this.value)"/> Roses <br />
<input type="radio" name="flowers" value="Carnations" onclick="setFlower(this.value)"/> Carnations <br />
<input type="radio" name="flowers" value="Daisies" onclick="setFlower(this.value)"/> Daisies <br />
<input type="button" name="displayButton" value="Request Info" onclick="displayMessage(this.value)" /> <br /><br />
<input type="text" name="thankyou" readonly="true" size="100" value="Thanks for using this program" />
</form>
</body>
</html>
Okay, now is where I'm stuck. The following exercise is as follows: The flower shop owner in the previous activity wants to see where you can make the form interactive and asks you to have the form display a message in the bottom text box that includes the user's name, a comma, and the words "thank you for your inquiry about" followed by the flower name the user selected. Write a function named displayMessage() that accesses the user's name from the first text box and displays the message in the read-only text box. You also need to make the Request Info button call the displayMessage() function when it's clicked. Using Javascript, make this form active by including event triggers and functions. My teacher has said that I should be able to do this by just referencing these two previous pages of code that I have already pasted. I feel like I am missing something, that I need to be doing something and it's just not working for me. I'm actually really really stuck on this. I haven't even gotten to the second half of the exercise (where I have to have it display about what flower you select) because I cant get this function to work. What am I missing? Also, the exercise we did before these two had us make a very basic account class and object. We don't have to do that at all in this anywhere, but I do know how to do it, in case I need to make a class or something. ANY AND ALL HELP GREATLY APPRECIATED!!! I just don't know what I'm supposed to do, I can't get it to work. Hi! I'm as new as they come when it deals with website development but forums have been useful to me in the past and I'm hoping I can get some kind of direction from all the wonderful people on this forum! I have an idea for a website that I'd like to pursue, and it would need functions such as: -Live news feed -Member logins, profiles, ability to rate/leave feedback for members -Mobile phone friendly -Comment on postings -Create an intro video (maybe even with animated stick figures to explain how the site works) -Accept paypal or other payment method -And basically, need to understand the monthly maintenance cost of all these functions, how to minimize expenses, etc. I know it seems far fetched for a newbie! But I need to know if this is possible.. how would I begin implementing a site like this.. Do I need to find a programmer to code it from scratch? Are there pre-written scripts available for all the functions I listed? What can I expect the costs to be? What's the best way to move forward? Can someone please tell me why there is an error with my code (see in red below). I am told that 'process' is not an object or is null and I don't understand why or the implications with the click event which I am trying to capture and pass to my function: Javascript Code: Code: var USStates = new Array(50);
USStates[0] = "Alabama";
USStates[1] = "Alaska";
USStates[2] = "Arizona";
USStates[3] = "Arkansas";
USStates[4] = "California";
USStates[5] = "Colorado";
USStates[6] = "Connecticut";
USStates[7] = "Delaware";
USStates[8] = "Florida";
USStates[9] = "Georgia";
USStates[10] = "Hawaii";
USStates[11] = "Idaho";
USStates[12] = "Illinois";
USStates[13] = "Indiana";
USStates[14] = "Iowa";
...
var stateEntered = new Array(50);
stateEntered[0] = "1819";
stateEntered[1] = "1959";
stateEntered[2] = "1912";
stateEntered[3] = "1836";
stateEntered[4] = "1850";
stateEntered[5] = "1876";
stateEntered[6] = "1788";
stateEntered[7] = "1787";
stateEntered[8] = "1845";
stateEntered[9] = "1788";
...
var process = document.getElementById("search");
process.onclick = getStateDate;
function getStateDate()
{
var selectedState = document.getElementById("entry").value;
for (var i = 0; i < USStates.length; i++)
{
if (USStates[i] == selectedState)
{
break;
}
}
if (i < USStates.length)
{
alert(selectedState + " entered the Union in " + stateEntered[i] + ".");
} else
{
alert("Sorry, '" + selectedState + "' isn't a US State.");
}
}
HTML Code ( in case you need it): Code: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>Loops</title> <script type="text/javascript" src="loops.js"></script> </head> <body> <h2>Enter a US Sate in the field below and click the 'submit' button to get the date of entry in the union</h2> <form action="process.php"> <input type="text" id="entry" name="entry" /> <input type="button" id="search" name="search" value="submit" /> </form> </body> </html> I wrote a log function that took note of various function calls. Thinking that functions are first class objects, and objects have properties, I made the name of each logged function a property of that function, e.g., brightenInnerPara.name = "brightenInnerPara"; Every browser I tried (Firefox, MSIE, Opera, Chrome, Safari) accepted the assignment, no problem. In Firefox and MSIE, the result was what I wanted: brightenInnerPara.name == "brightenInnerPara" But in the others, the result was: brightenInnerPara.name == null Question 1. Which Javascript is correct here? I favor Firefox and MSIE, not merely because they were willing to give me what I wanted, but also because it makes no sense to accept an assignment statement without throwing an error and then give it a null semantics, like Chrome, Opera, and Safari did. I found a workaround, using assignments like this: brightenInnerPara.prototype.name = "brightenInnerPara"; To my surprise, that worked in every browser. But I don't know why. It seems that such assignments are enough to cause each function to have its own distinct prototype. Question 2. Just how inefficient is my workaround, and why does it work? I want to learn javascript and I found codecademy.com which seems like a great way to learn the language. Before the first lesson it says Quote: You should be comfortable with loops, if statements, functions, and objects before attempting this course. Can someone explain what these are or point me in the direction where I can find the answers? I tried searching with google, but I havent found anything that clearly states what exactly the loop, object, etc. is. I'm in a computer coding class, and I'm having a bit of trouble with Javascript. I'm not looking for anyone to do my homework for me, but any hints you could give me as to why this code isn't working would be greatly appreciated. Basically, I need an empty text box where the user enters their guess as to my age. The user enters their guess, and then gets an answer as to whether their guess is right, too high, or too low. The page looks right, but I can't get the function to work. Thank you... <html> <head> <script> function howoldami(age) if(age=23) { alert("You guessed right!"); } else if { (age>23) alert("I'm not that old."); } else { alert("I'm not that young."); } </script> </head> <body> <form> Guess My Age!<input name="age"><br> <input type=button value=Guess! onclick="howoldami(age.value)"> </form> </body> </html> This is what I am aiming for. I want to be able to click on a word that would then write text in a specified area. This is what I came up with but it writes it at the top of the page and only for a moment then disappears.... These are my clickable words Code: <a href="#textarea" onClick="MathHomework('W2')">Week 2</a>
<a href="#textarea" onClick="MathHomework('W3')">Week 3</a>
the anchor named 'textarea' is where I want the output to be written which is placed on my html page. This is my newbie script Code: <script type="text/javascript">
function MathHomework(week) {
if (week == "W2")
document.write("<p>Review Chapter Twelve</p>");
else if (week == "W3")
document.write("<p>Final Chapter Review Test</p>");
}
</script>
<a name="textarea"> (text area for javascript output)</a>
so is my onclick syntax wrong maybe? and yes I have read rule#5 and I am trying to understand my mistakes. Thank you in advance Hi! Im new to the world of javascript, so bare with me. It might be a stupid question but i got a input form, i know how to get the data in but i need to single out one of the numbers. the input looks like: xxxxxx-xxxx I've tried almost everything that i can think of... A nudge in the right direction would be appreciated. Hello, I'm in the process of getting a better understanding of javascript (instead of just copying and pasting JQuery script onto my site). So I have a(dumb?) question. Can I name a var what ever I want? For example, var car_name("Ford Escape"); Or am I misunderstanding this? THanks. Thinking in Objects 4 objects w/constructors/overloads min 3 properties on each min 3 methods total was just wondering if anyone had any good links or tutorials to get me started on my first javascript assignment Hi Everyone I'm learning Javascript with varying degree's of success but am very much in the early phase. My question/problem is this: [ICODE]<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>Untitled Document</title> </head> <body> <script language="javascript" type="text/javascript"> var degFahren = new Array(212, "string data", -459.67); var degCent = new Array(); var loopCounter; for(loopcounter =0; loopCounter <= 2; loopCounter++){ if(isNaN(degFahren[loopCounter])){ alert("Data " + degFahren[loopCounter] + " at array index " + loopCounter + " is invalid"); continue; } degcent[loopCounter] = 5/9 * (degFahren[loopCounter] -32); } for (loopCounter =2; loopCounter >=0; loopCounter --){ document.write("Value " + loopCounter + " was " + degFahren[loopCounter] + " degrees Fahrenheit"); document.write(" which is " + degCent[loopCounter] + " degrees centigrade<br />"); } </script> </body> </html> /ICODE] The following code does not return any errors in my browser but I'm confused since I'm sure I should be seeing an alert box telling me that there is invalid data entered bu this doesn't happen, also as far as I can make out I should only be receiving an error for the 2nd loop but there seem to be an error message returned for all 3 loops?? This is all possibly correct but I'm learning from a book and I have no-one to ask these mundane questions to. Any help would be greatly received. Sara Hi, I am just beginning out with Javascript and trying to complete a simple login page. Clicking on the Login button should bring up a message 'Access authorised' or 'Access denied' in the 'output' div of the page. Unfortunately only 'Access Denied' displays, even if the password entered is correct. There are no messages displayed in the Error Console. Any advice greatly appreciated! Code: <html>
<head>
<title>Function Example</title>
<script language="javascript" type="text/javascript">
function isAccessAuthorised(enteredPassword)
{
var result;
if(enteredPassword=="password")
{
result=true;
}
else
{
result=false;
}
return result;
}
function buttonClicked()
{
var isAuthorised = isAccessAuthorised("enteredPassword").value;
if(isAuthorised==true)
{
document.getElementById("output").innerHTML=<p>Access authorised</p>;
}
else
{
document.getElementById("output").innerHTML=<p>Access denied</p>;
}
}
</script>
</head>
<body>
<form>
<input type="text" id="username" /> <br/>
<input type="text" id="enteredPassword" /> <br/>
<input type="button" onClick="buttonClicked()" value="Login">
</form>
<div id="output">
</div>
</body>
</html>
I have yet to have my ah-ha moment with Javascript but I think its coming soon. there are small things that seem to be baffling me and Im hoping posting to the forums to get help from people of limitless wisdom. What exactly does the "|" mean in this code? or I should say what does it do? Code: document.template.Aprod_string.value = document.template.Aprod_string.value + "|" + string_recode(Aprod_array) ; |
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