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      GameDev.net and CRC Press have teamed up to bring a free ebook of content curated from top titles published by CRC Press. The freebook, Practices of Game Design & Indie Game Marketing, includes chapters from The Art of Game Design: A Book of Lenses, A Practical Guide to Indie Game Marketing, and An Architectural Approach to Level Design. The GameDev.net FreeBook is relevant to game designers, developers, and those interested in learning more about the challenges in game development. We know game development can be a tough discipline and business, so we picked several chapters from CRC Press titles that we thought would be of interest to you, the GameDev.net audience, in your journey to design, develop, and market your next game. The free ebook is available through CRC Press by clicking here. The Curated Books The Art of Game Design: A Book of Lenses, Second Edition, by Jesse Schell Presents 100+ sets of questions, or different lenses, for viewing a game’s design, encompassing diverse fields such as psychology, architecture, music, film, software engineering, theme park design, mathematics, anthropology, and more. Written by one of the world's top game designers, this book describes the deepest and most fundamental principles of game design, demonstrating how tactics used in board, card, and athletic games also work in video games. It provides practical instruction on creating world-class games that will be played again and again. View it here. A Practical Guide to Indie Game Marketing, by Joel Dreskin Marketing is an essential but too frequently overlooked or minimized component of the release plan for indie games. A Practical Guide to Indie Game Marketing provides you with the tools needed to build visibility and sell your indie games. With special focus on those developers with small budgets and limited staff and resources, this book is packed with tangible recommendations and techniques that you can put to use immediately. As a seasoned professional of the indie game arena, author Joel Dreskin gives you insight into practical, real-world experiences of marketing numerous successful games and also provides stories of the failures. View it here. An Architectural Approach to Level Design This is one of the first books to integrate architectural and spatial design theory with the field of level design. The book presents architectural techniques and theories for level designers to use in their own work. It connects architecture and level design in different ways that address the practical elements of how designers construct space and the experiential elements of how and why humans interact with this space. Throughout the text, readers learn skills for spatial layout, evoking emotion through gamespaces, and creating better levels through architectural theory. View it here. Learn more and download the ebook by clicking here. Did you know? GameDev.net and CRC Press also recently teamed up to bring GDNet+ Members up to a 20% discount on all CRC Press books. Learn more about this and other benefits here.
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Jethro_T

Basic Javascript and Html

2 posts in this topic

I'm trying to learn some web programming and just spent hours trying to get the most basic javascript working. I don't understand where I'm going wrong, I've downloaded similar examples to the code I wrote and they work fine but my own javascript does not work at all! I would really appreciate if someone could take the time to try to help me figure out what I'm doing wrong.

event.js
[source]
document.getElementById("width").onchange = checkDimensions;
[/source]

checkDim.js
[source]
function checkDimensions() {
document.getElementById("width").value = "HELLO";
return false;
}
[/source]

index.html
[source]
<?xml version = "1.0" encoding = "utf-8" ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "[url="http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"]http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd[/url]">
<html xmlns = "[url="http://www.w3.org/1999/xhtml"]http://www.w3.org/1999/xhtml[/url]">
<head>
<title>Canvas Printing Calculator</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
<link rel="stylesheet" href="style.css"/>
<script type="text/javascript" src="event.js">
</script>
</head>
<body>
<form action="">
<input type="text" id="width" size="30"/>
</form>
</body>
<script type="text/javascript" src="checkDim.js">
</script>
</html>
[/source]
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The document, including the Javascript, is parsed and executed top-down. When your file [i]event.js[/i] is loaded, it is executed, but at that point there is no element with id "[i]width[/i]" yet. You need to execute that line after the element with id "[i]width[/i]". You also need to ensure that the function [i]checkDimension [/i]actually exists at the point that you are installing the onchange callback. At this point, the error is that [i]checkDimension [/i]is an unknown symbol, because it will be loaded later into the document.

The way to do these things is to not execute the initialization code until the document has been entirely loaded. Install a callback function to the [i]onload [/i]property of [i]window [/i]or [i]document[/i], which will be called when the whole document (which includes the presence of the element with the "[i]width[/i]" id, and the [i]checkDimension [/i]function).
[code]
window.onload = function() {
document.getElementById("width").onchange = checkDimensions;
}
[/code]
It creates an anonymous function and assigns it to the [i]onload [/i]callback. When the document has finished loading, it is called so you can install the callback to the desired element.
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Alternatively

[code]
document.addEventListener("DOMContentLoaded", function () {
document.getElementById("width").onchange = function() {
this.value = "HELLO";
return false;
}
}
[/code]

The advantage of DOMContentLoaded is that it executes as soon as the DOM has loaded, where as window.onload will wait until [i]all[/i] content has finished loading. If your page has images and ads, this means your code could get to execute much sooner.
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