test-settimeout-simple

setTimeout() caveats or misunderstanding. What is real timeout value?

Usage:

To install locally go in the root directory of your project and type

npm install test-settimeout-simple --save-dev

or

npm -i test-settimeout-simple --save-dev

Test from console:

npm test <delay> <timeout>

where
delay and timeout are digital variables with meanings:
timeout - number of milliseconds similar to second argument of JavaScript setTimeout() function.
delay - presumable calculation time in milliseconds necessary to carry out codes in js-block following after the line where setTimeout() function is calling Example:

npm test 100 500

or

npm test 500 200

To get equivalent tests inside your project module:

var simp = require('test-settimeout-simple').simple;
simp.test(100,500);
simp.test(500,200);

See codes and printing output for details comprehension.

Pretext:

I observed that effective timeout (lag of launching) of argument-function in standard JavaScript setTimeout(fun, timeout) depends on the time necessary to carry out calculation of codes following the line where setTimeout() resides, i.e.

By definition

{
  // ...
  t0 = new Date();
  var cleaner = setTimeout(fun,timeout);  

means that function fun will be launched over approximately timeout milliseconds. Suppose that after this statement we have a block consuming time for it's calculation, like this

 var t = 0, tw;  
  while( t < delay ){    
    tw = new Date();
    t = tw - t0;
  }

'delay' milliseconds will be consumed by this.

The effective timeout over which fun will begin to run will be equal to timeout argument's value only if timeout >= delay

Otherwise the delay's value determines effective timeout.

Testing code used:

var cleaner,
    ob = { 
      tf: undefined  //  fun's run beginning time      
    }; 
/** 
 * setTimeout() function-argument
 */
function fun(){
  var tf = new Date();
  ob.tf = tf.getTime();
  
  console.log('in fun: tf = %s, (tf - t0) = %s',
      ob.tf,
      ob.tf - ob.t0);
 
  clearTimeout(cleaner);
}   
/** 
 * test function 
 * @param {number} delay of process's flow in [milliseconds] 
 * @param {number} timeout value of setTimout()'s second argument 
 */
function test( delay, timeout ){
  console.log('test goes ...');
  var tw,      
      t0 = new Date();
  ob.t0 = t0.getTime();
  
  cleaner = setTimeout(fun,timeout);
  
  var t = 0;  
  while( t < delay ){    // process lag
    tw = new Date();
    t = tw - t0;
  }  
  console.log('finish of test with\n' +
              'delay: %s\n' +
              'timeout: %s\n' +  
              't0 = %s\n' +
              'tw = %s\n' +                                   
              't = %s',
              delay, timeout,
              t0.getTime(),tw.getTime(), t
              );  
}

Table bellow illustrates testing results used codes from repository https://github.com/vuGitH/test-settimeout-simple :

in node.js REPL

| delay | timeout | effective timeout | |-------|-------|---------------------| | 1000 | 1000 | 1011 | | 1000 | 1000 | 1007 | | 50 | 50 | 56 | | 50 | 50 | 56 | | 100 |2000 | 2007 | | 200 | 5000 | 5001 | | 500 | 100 | 502 | | 1000 | 100 | 1007 | | 1000 | 50 | 1007 | | 1000 | 50 | 1005 | | 1000 | 50 | 1006 | | 2000 | 50 | 2006 | | 2000 | 50 | 2006 | | 2000 | 50 | 2006 | | 4000 | 50 | 4006 | | 4000 | 50 | 4006 | | 4000 | 3000 | 4007 |

in Google Chrome console

| delay | timeout | effective timeout | |-------|-------|---------------------| | 1000 | 1000 | 1003 | | 1000 | 1000 | 1001 | | 50 | 50 | 51 | | 50 | 50 | 52 | | 100 |2000 | 2000 | | 200 | 5000 | 5001 | | 500 | 100 | 502 | | 1000 | 100 | 1004 | | 1000 | 50 | 1002 | | 1000 | 50 | 1002 | | 1000 | 50 | 1002 | | 2000 | 50 | 2001 | | 2000 | 50 | 2001 | | 2000 | 50 | 2001 | | 4000 | 50 | 4003 | | 4000 | 50 | 4001 | | 4000 | 3000 | 4006 |

in MSE console

| delay | timeout | effective timeout | |-------|-------|---------------------| | 1000 | 1000 | 1003 | | 1000 | 1000 | 1004 | | 50 | 50 | 53 | | 50 | 50 | 56 | | 100 |2000 | 2004 | | 200 | 5000 | 5011 | | 500 | 100 | 505 | | 1000 | 100 | 1004 | | 1000 | 50 | 1006 | | 1000 | 50 | 1003 | | 1000 | 50 | 1003 | | 2000 | 50 | 2005 | | 2000 | 50 | 2001 | | 2000 | 50 | 2006 | | 4000 | 50 | 4003 | | 4000 | 50 | 4002 | | 4000 | 3000 | 4002 |

Comments or editions Welcome! Vladimir Uralov [email protected]