Wikibooks

JavaScript/Shell

< JavaScript



You can play around with JavaScript in one of multiple shells, in interactive batch mode. This means that you can enter JavaScript one line at a time and have it immediately executed; and if you enter a statement that returns a value without assigning the value anywhere, the value is displayed.

For a list of shells, see the mozilla.org list referenced from Enternal links.

Keywords: REPL.

Standalone

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Mozilla Firefox uses SpiderMonkey JavaScript engine, which is available as a standalone interactive shell for multiple platforms. You can download it from:

Unzip the file, and run "js" from the command line. A prompt appears: 

js>

You can enter statements, one at a time: 

js> function incr(i) { return i+1; }
js> incr(1)
2
js> function plus2(i) {
return i+2;
}
js> plus2(1)
3
js> incr
function incr(i) { return i+1; }
js> print ("1+1:"+incr(1))
1+1:2
js> console.log("Yep.") // Console is available
Yep.

Multi-line function definitions can be entered one line at a time, pressing enter after each line.

To run JavaScript snippets that use alert function--since they are intended for web browsers, you can define your own alert function: 

js> function alert(message) { print ("Alert: "+message); }

From browser

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You can have an interactive mode, entering JavaScript one line at a time and have it immediately executed, directly from your web browser.

In many versions of Firefox, press Control + Shift + K to get a web console window. At the bottom of the console window, there is a separate one-line field into which you can enter JavaScript lines and have them run by pressing Enter. Even multi-line function definitions can be entered, but not by pressing Enter but rather Shift + Enter and pressing Enter only after the whole definition was entered.

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