slow down execution of javascript's eval

Question

I have created a little robot like the Karel robot (Wikipedia) which is based on javascript.

The robot can be controlled with some simple commands such as "forward", "turnright" and so on.

The user can write a javascript program to control the robot which then goes through javascripts "eval()" function so that the robot moves.

The problem is that I want the robot to move slowly so that you can see what he is doing and so that you can highlight the current code line in the editor.

Current method: Parsing

At the moment I have solved this (in the offline version) by parsing each line in the textarea and then building a stack of action which are then executed one after another with window.setTimeout. But this is of course limited because I have to write parsing code for every little javascript language contruct which is much work and error prone.

Some additional information to this:

Parsing version: http://abi-physik.de/_niki2/niki.php

Parsing version js code: http://abi-physik.de/_niki2/js/niki.js

Important functions are at the bottom of the script: run(), execute()

I am currently parsing the user script line by line and adding the actions to a stack. If the parser encounters an "if" it will begin a new stack and add all actions to that stack. if the parser then encounters an "}" it will close the "if" stack and continue to add actions to the base stack.

Any idea to improve this?

Have you tried splitting lines on ";" or \n then passing to eval one by one — Pradeep, Aug 03 '11 at 09:38
I thought about it, but I did not try it yet. What will happen to if-conditions? — Dennis Keil, Aug 03 '11 at 10:35
In this case also you will have to implement things for if , while loop. You can combine them into single code block but it will not show animation. — Pradeep, Aug 03 '11 at 11:13
Edited your post to fix the URLs for you, as they're clearly relevant, so deserve to be proper links — David Precious, Aug 03 '11 at 11:24
Are you planning on having nested whiles and for loops? `while( while() )` — epascarello, Aug 03 '11 at 11:53
@epascarello Yes I plan on having nested loops and if-conditions and I have updated the parsing algorithm so that it seems to work (no for loop yet). — Dennis Keil, Aug 03 '11 at 14:09

score 1 · Accepted Answer · answered Aug 03 '11 at 11:37

I would say have those functions register to some queue instead of having them execute the JavaScript directly.

var moveQueue = [];

function forward(){
  moveQueue.push(_forward);
}
function _forward(){
    alert("move forward");
}

function backward(){
  moveQueue.push(_backward);
}
function _backward(){
    alert("move backward");
}

Than when it runs you would use a setTimeout and

function run(){
    var curStep = 0;
   function go(){
      moveQueue[curStep]();
      curStep++;
      if(curStep<moveQueue.length){
          window.setTimeout(go,500);
      }
   }  
}

You still would need to parse it out to figure out the if statement logic, but this is one of many ways that will allow you to control the speed of execution.

score 0 · Answer 2 · answered Aug 03 '11 at 09:40

0

Javascript doesn't have a sleep() function, so yes, using setTimeout or setInterval is the way to go.

You could parse the 'instructions' first, assemble an array of actions that need to be carried out, then use setInterval to arrange for a function to be regularly called which takes the next instruction and carries it out (or clears the interval, if there are no more instructions waiting to be processed).

answered Aug 03 '11 at 09:40

David Precious

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That's roughly what I am doing (see js code, I have updated the question). The problem is that I have to implement things as while-loop, for-loop, functions and so on which is much work and error prone. – Dennis Keil Aug 03 '11 at 10:34

slow down execution of javascript's eval

2 Answers2