Online JavaScript Interpreter: Programming anywhere, nothing to install, works in any browser
Type your JavaScript program into the box below. Then click the Run button to see the result. To save your work, select the text and copy it to an editor or email it to yourself.
Type JavaScript     Examples:    Output     Timing: s
Note that this is dynamic code running locally on your machine. If you leave this page before copying and saving your work, it may disappear.

Quick reference to basic JavaScript commands. Search online for tutorials
Comment 
// this is a one-line comment
/* this comment could contain linebreaks */
Constant numbers 12.3 and strings "hi", "hi".charAt(0) is "h"
Variable start with a letter, then use letters, digits or _ (declared with var)
Expression built from +, -, *, /, pow(x,y), sqrt(), PI, E, log(), floor(), ceil(),
random(), sin(), cos(), tan(), atan() and constants, variables, functions
Assignment 
v = expression;
Block 
{   statement 1;
    ...
    statement n;
}
Condition expression == expression or <=, <, >, >=, !=...
or !cond, cond1 && cond2, cond1 || cond2
if - else 
if (condition) block 1
else block 2                   // optional
for-loop 
for (var i=start; endcondition; i++)
    block
while-loop 
while (condition) 
    block
Function 
f = function(v1, ..., vn) {
    statement 1;
    ...
    return expression;
}
List (array) 
a = [1,2,"hi"]
a[0] is 1, a.length is 3, a+[4] is [1,2,"hi",4]
Object
(hash tables)		 
object = {attribute:expression, method:function}
a = {x:2, y:3, s:function(){return this.x+this.y}}
a.x is 3, a["x"] is 3, a.s() is 5
Output 
write("Hello"); writeln(" world");

This page is useful for experimenting with basic JavaScript and simple algorithms (e.g. those covered in a discrete mathematics course). It should work in any browser that has JavaScript enabled (including smartphone browsers).

You can save your own local copy of this page (using Save As...), and use it even when you are not connected to the internet.

Peter Jipsen, January 2013, Chapman University