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CSCI 100
Think Like Computers
Lecture 15
Fall 2008
Last Time …
•JavaScript: THE scripting tool for
webpages
•For creating dynamic HTML webpages
(DHTML)
JavaScript Overview
•<script type=“text/javascript>
……. // script code here
</script>
•<body onUnload=“alert(‘Thanks for visiting!’);” >
•Variables
VARIABLE = prompt("PROMPT MESSAGE", "") ;
firstName = prompt("Please enter your name", "");
•Write to the web page:
document.write("MESSAGE TO BE DISPLAYED " + VARIABLE + "
MORE MESSAGE" + ...);
document.write("Hello " + firstName + ", welcome to my Web page. ");
Formatted Output
•the output produced by a write statement is embedded in
the page
the browser displays this output just as it does any other text
if the text contains HTML tags, the browser will interpret the tags and format the
text accordingly
document.write("Hello <i>" + firstName +
"</i>, welcome to my Web page.");
assuming the variable firstName has been assigned "Dave", the browser
would execute the statement to produce
Hello <i>Dave</i>, welcome to my Web p age.
which would be displayed by the browser as
Hello Dave, welcome to my Web page.
Syntax Errors
•an error in the format of an HTML or JavaScript
statements is known as a syntax error
some syntax errors are ignored by the browser
e.g., misspelling an HTML tag name
most JavaScript syntax errors will generate an error message
document.write("This example is illegal since the
string is broken across lines");
yields: Error: unterminated string literal
document.write("The value of x is " x);
yields: Error: missing ) after argument list
JavaScript Variables
•a variable name can be any sequence of letters, digits, and underscor es
(but must start with a letter)
valid: tempInFahr SUM current_age Sum2Date x
invalid: 2hotforU salary$ two words "sum_to_date"
•variable names are case sensitive, so Sum and SUM are treated a s different
variables
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