Javascript Ninja Central Timer中的时间在哪里？

Question

The Central Timer Control presented in Secrets of the Javascript Ninja executes the added functions as quickly as possible. How could I use this idea of Central Timer Control to have something happen every 250 ms? What if I needed one thing to happen every 250 ms and another thing to happen every 600 ms? I feel like I've really missed the boat here, somehow.

Answer 1

Sorry, I didn't have much time to write good readable code but if you run this script and walk it in the debugger you'll get an idea how to implement what you want in the single threaded environment. Please note that solution that uses Web Workers would probably work better if you want to make sure that you'll get one function shouting every 250ms and another 650ms, but that, I think, can't be called Central Timer Control anymore.

If you pass 300 to the delay function of the function 'one' you'll see why this method doesn't always work.

BTW Secrets of the Javascript Ninja is the best book about JavaScript that I've ever read. Good choice.

       var fns = [];

        function delay(ms) { // you can set delay manually to see what happens if functions take longer to execute
            ms += new Date().getTime();
            while (new Date() < ms){}
        } 


        var one = function(d) { // first function
            console.log(new Date() - temp);
            temp = new Date;
            delay(100); // let's say our function takes approximately 100 ms to execute
        }

        var two = function(d) { // second function
            console.log(new Date() - temp);
            temp = new Date;
            delay(150);

        }

        fns.push(one);
        fns.push(two);

        intervals = [250, 650];

        var temp = new Date;
        (function(fns, intervals) {
        var count = 0,
            start, finish, execTime; // helpers
        (function run () {
            start = new Date();
            fns[count](); // function executes here
            finish = new Date();
            execTime = finish - start; // time that function takes to execute
            setTimeout(run, ( (intervals[count] - execTime) > 0) ? intervals[count] - execTime : 0 ); // if function took too long to execute start as soon as you can, otherwise subtract execution time from the interval
            if (count === intervals.length - 1) {
                count = 0;
            } else {
                count++;
            }
        })()

        })(fns, intervals) // passing array of function to execute and array of intervals