When this tutorial was first written, there was little other than "document.write" to make changes on the fly in webpages. After a page has been opened, then document.write cannot be used to change the page. The best way to change a page dynamically is to use DOM. You might want to start with getElementById.
When we used the first prompt example, we ended up with a page with the name we entered in the prompt written in the page. Something funny was going on there. Here's the code:
Name1=prompt("What is your name Enter a name in the box "+
"so you can see the effect on the page","Fido");
document.write("<h1>"+Name1+"\'s Special Page</h1>");
document.write("Welcome to my page ");
document.write("I have made everything just right for you.");
document.write("<p>So, "+Name1+", click <a href='index.html'>here</a> "+
"to learn how to get what you have been dreaming of for so long!<hr>");
The page has a function called Info(). First this launches a prompt message to get the user's name, or whatever they might type. The default name is Fido. If nothing is entered in the prompt box, the name Fido will be used. Whatever is in the input part of the prompt box is stored in the variable Name1.
Note: The text block, by the way, is broken using the quotation marks and the + sign (who said concatenation operator? Order them out at once!) This just stops possible problems with unterminated string errors in advance.
Then the Java Script begins to write stuff. The first line is:
document.write("<h1>"+Name1+"\'s Special Page</h1>")
The document dot write bit, followed by the first bracket and the quotation mark, writes whatever follows. Here it writes the HTML header (in quotes) plus the variable, Name1, which contains the user's name. The variable is not in quotes because we do not want the computer to print 'Name1', which it would if we put it in quotes. We want it to print the value it contains, here the user's name.
Next, in quotes, we have the back slash followed by an apostrophe. We use the backslash (\) to tell the code we are still entering text, and not ending the string. After more text, we end this string by writing the quotation mark and the end bracket. From here the computer sallies forth and writes whatever we have told it, HTML code and all!
Well, I suppose, you are saying do you really have to write all those document writes? Wouldn't one do? And what if you want Java Script to write somewhere other than at the start of the page? All right then, let's look at writing where you like!
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