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JavaScript
Informatics for economists I
Introduction
Programming language used in web pages.
Simple and easy to use – written in HTML document.
Client scripting language – script is sent with HTML document to web browser (client).
JS is not Java. It has just similar syntax.
Characteristics
Interpreted lang. – no compiling Object oriented – uses web browser
and built-in objects Browser dependent Case sensitive Syntax is similar to C or Java
language.
Limitations
Works in web browser only. User can disable JS in browser. Many different JS versions. Cannot access to files or system
object. Cannot save data.
Writing JS scripts
Use <script> </script> tags. Example:
<body>
<script>
document.write(“Hello world!”);
</script>
</body>
JS variables
Initialized when firstly used. Case sensitive Example:
var x, y;
x=10;
y=”Hallo”;
JS operators
value assignment:
=
numeric operators:
+, -, *, /
logical operators:
==, !=, <, >, <=, >=
Conditions
Used to decide whether the expression is true or not
if (expression) {commands when true;
} else {commands when false;
}
Cycles
Used to repeat commands.while (expression) {
commands;
}
for (initial value, condition, increment){
commands;
}
Functions
Frequently used part of program
function name(params){
commands;
return value;
}
Object document
Most frequently used object in JS. Contains everything on the page.
document.forms
document.images
Object Math
Used with mathematical operations
Math.abs(x)
Math.exp(x)
Math.pow(a,x)
Math.sqrt(x)
Math.PI
Events
Activated when user does actiononLoad – loading document
onClick – cliking on object
onDblClick – doubleclicking on object
onMouseOver – move mouse over object
onMouseOut – move mouse out of object
onFocus – focusing object (activating)
onKeyPress – pressing key on object
onSubmit – pressing submit form button
Communication with user
Print information: alert(“some text”); document.write(“some text”);
Get data from user: prompt(“prompt text”,”initial value”);
parseInt, parseFloat Use forms:
<input type=”text” name=”id”>
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