setTimeout not working in windows script (jscript)

问题:

When I try to run the following code in my program

setTimeout("alert('moo')", 1000);

I get the following error

Error: Object expected
Code: 800A138F
Source: Microsoft JScript runtime error

Why? Am I calling the wrong function? What I want to do is delay the execution of the subsequent function.

回答1:

It sounds like you're using setTimeout in a non-browser-based script (Windows Script Host or similar). You can't do that. You can, however, use WScript.Sleep to suspend your script briefly, with which you can achieve a similar effect. Also, alert is not a WSH function; you may want WScript.Echo. More on the WSH reference on MSDN.

回答2:

setTimeout is a method of the window object provided by web browsers. It's not available to scripts running on Windows Script Host. Those scripts have a single thread of execution from start to finish and have no delay timers.

If you want to pause script execution you can use the Sleep method of the WScript object.

回答3:

I needed WSH to behave like similar code in browser that uses setTimeout, so here's what I came up with.

Just have your single thread execute everything in a queue. You can keep adding to the queue. The program will only terminate when no functions are left in the queue.

It doesn't support strings for eval, just functions.

function main() {
  Test.before();
  _setTimeout(Test.timeout1, 1000);
  _setTimeout(Test.timeout2, 2000);
  _setTimeout(Test.timeout3, 500);
  _setTimeout(Test.error, 2001);
  Test.after();
}

var Test = function() {
  var ld = "---- ";
  var rd = " ----";
  return {
    before : function() {
      log(ld + "Before" + rd);
    },
    after : function() {
      log(ld + "After" + rd);
    },
    timeout1 : function() {
      log(ld + "Timeout1" + rd);
    },
    timeout2 : function() {
      log(ld + "Timeout2" + rd);
    },
    timeout3 : function() {
      log(ld + "Timeout3" + rd);
    },
    error : function() {
      log(ld + "error" + rd);
      errorFunc();
    }
  };
}();

var FuncQueue = function() {
  var funcQueue = [];
  function FuncItem(name, func, waitTil) {
    this.name = name;
    this.func = func;
    this.waitTil = waitTil;
  }
  return {
    add : function(func, name, waitTil) {
      funcQueue.push(new FuncItem(name, func, waitTil));
    },
    run : function() {
      while (funcQueue.length > 0) {
        var now = new Date().valueOf();
        for ( var i = 0; i < funcQueue.length; i++) {
          var item = funcQueue[i];
          if (item.waitTil > now) {
            continue;
          } else {
            funcQueue.splice(i, 1);
          }
          log("Executing: " + item.name);
          try {
            item.func();
          } catch (e) {
            log("Unexpected error occured");
          }
          log("Completed executing: " + item.name);
          break;
        }
        if (funcQueue.length > 0 && i > 0) {
          if (typeof (WScript) != "undefined") {
            WScript.Sleep(50);
          }
        }
      }
      log("Exhausted function queue");
    }
  }
}();

function _setTimeout(func, delayMs) {
  var retval = undefined;
  if (typeof (setTimeout) != "undefined") {
    retval = setTimeout(func, delayMs); // use the real thing if available
  } else {
    FuncQueue.add(func, "setTimeout", new Date().valueOf() + delayMs);
  }
  return retval;
}

var log = function() {
  function ms() {
    if (!ms.start) {
      ms.start = new Date().valueOf();
    }
    return new Date().valueOf() - ms.start; // report ms since first call to function
  }
  function pad(s, n) {
    s += "";
    var filler = "     ";
    if (s.length < n) {
      return filler.substr(0, n - s.length) + s;
    }
    return s;
  }
  return function(s) {
    if (typeof (WScript) != "undefined") {
      WScript.StdOut.WriteLine(pad(ms(), 6) + " " + s);
    } else {
      // find a different method
    }
  }
}();

FuncQueue.add(main, "main");
FuncQueue.run();

回答4:

For anybody who is searching for the alert function to work in a stand-alone script (Windows Script Host environment), I recommend checking out jPaq's alert function which is documented here and downloadable here. I have definitely found this new library to be helpful for my stand-alone scripts.