Change speed of timedLoop with a variable

CS Principles Coding and Debugging Help
1

Is it possible to change the speed of a timedLoop after it starts? For e.g. in the project below, i want the timedloop to trigger at a speed controlled elsewhere (when the score increments by 5)

Link to the project or level: https://studio.code.org/projects/applab/KJJvN7kxYUDD9IrRQ1wXWrIZK3rPy5Gff-umf4f1kTE/edit

What I expect to happen: Change speed of bug moving

What actually happens: same speed

What I’ve tried: looked at the docs

2

You can’t change the speed of a timedLoop (setInterval) once it’s called. You could however use a recursive function that calls itself after a certain period of time.

var speed = 1000
function step(){
    console.log("step!")
    delay(speed, step) --calls step again after *speed* milliseconds
}
step()
1 Like
3

Javascript, which App Lab is based on, is call by value. Meaning that when you call a function like timedLoop the value of the variables are sent as parameters to the function and not a reference to the variable. When you send the variable itself as a parameter that is call by reference.

So, call by value only sends the value. If you change the value of the variable it doesn’t do anything because timedLoop has the old value. timedLoop doesn’t know nor care about the variable speed.

What you need to do is stop the loop and start it again after you change speed. Look at this for example:

var score = 0;
var lives = 3;
var bugSpeed = 1000;

onEvent("image2", "click", function() {
  lives = lives - 1;
  setText("lives_lbl", lives);
  if (lives < 1) {
    stopTimedLoop();
    setScreen("screen2");
  }
});

onEvent("bug", "click", function () {
  score = score + 1;
  setProperty("score_lbl", "text", score);
  if (score % 3 == 0 && score > 0) {
    changeBugSpeed();
  }
});

function startMovingBug () {
  timedLoop(bugSpeed, function () {
    setProperty("bug", "x", randomNumber(1, 299));
    setProperty("bug", "y", randomNumber(50, 400));
  });
}

function changeBugSpeed () {
  bugSpeed = bugSpeed * 0.8;
  stopTimedLoop();
  startMovingBug();
}

startMovingBug();

First, I changed speed to bugSpeed because you found a bug in App Lab. Nice.

I made the startMovingBug function. I can use this to start the bug up. I also moved the game-over-test to just below where the lives are set. Checking the lives right after you change them removes a little delay between losing the last life and the game over screen. But more importantly it takes the game over logic out of the timed loop so the timed loop code is easier to understand.

I made the changeBugSpeed function which changes the speed, stops the previous loop, then starts a new loop but moving faster.

At the bottom of the code I added a call to startMovingBug to start the game going.

Functions are your friends let them help you.

1 Like
4

Thanks a lot, Don - appreciate your input on functions.

how did i find a bug though?

5

speed is already declared as a variable in the global context. That should not happen.