monitor.js

/*

    monitor.js - monitors a javascript file and re-executes when file is
    saved. eg:
    
    $ node monitor.js /home/me/sample.js
    
    Now edit /home/me/sample.js and watch the console output. Like a "live
    firebug", though gives you the comfort of your own editor for quick 
    testing and prototyping. 

*/

var path = require("path"),
    fs = require("fs"),
    vm = require("vm")
;

if(process.argv.length < 3){
    process.quit();
}

var file = process.argv[2];

function run(file){
    fs.readFile(file, "utf8", function(error, content){
        if(!error){
            try{
                console.log("-- RUNNING:", file);
                vm.runInThisContext(content);
                console.log("-- COMPLETE!");
            }catch(e){
                console.log(e.stack);
            }
        }
    });
}


file && path.exists(file, function(exists){
    
    if(!exists){
        console.log("ERROR: file not found:", file);
        return;
    }
    
    fs.watchFile(file, function(cur, prev){
        if(cur.mtime > prev.mtime){
            run(file);
        }
    });
    
    run(file);
    
});