Math.wrap

[espruino-discuss]

Posted at 2018-01-14 by Frida

I have problems with Math.wrap.
When I run it in a program, it does not wrap, but if I enter it in the console it wraps it ok.

// test.js

var tmp = [];
var i = 0;
var k = 0;

function onInit() {


  for(var j = 0; j < 30; j++) {
    tmp[i] = i;
    console.log('k = ' + k +'  ' + 'i = ' + i);
    Math.wrap(k++, 10);
    i++; if(i > 9) {i = 0;}


  }

  console.log(tmp);
  console.log(tmp.length);


}
setTimeout(onInit, 100);

/*
k = 0  i = 0
k = 1  i = 1
k = 2  i = 2
k = 3  i = 3
k = 4  i = 4
k = 5  i = 5
k = 6  i = 6
k = 7  i = 7
k = 8  i = 8
k = 9  i = 9
k = 10  i = 0
k = 11  i = 1
k = 12  i = 2
k = 13  i = 3
k = 14  i = 4
k = 15  i = 5
k = 16  i = 6
k = 17  i = 7
k = 18  i = 8
k = 19  i = 9
k = 20  i = 0
k = 21  i = 1
k = 22  i = 2
k = 23  i = 3
k = 24  i = 4
k = 25  i = 5
k = 26  i = 6
k = 27  i = 7
k = 28  i = 8
k = 29  i = 9
[ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ]
10
>k
=30
>Math.wrap(k++, 10)
=0
>Math.wrap(k++, 10)
=1
>Math.wrap(k++, 10)
=2
>Math.wrap(k++, 10)
=3
>Math.wrap(k++, 10)
=4
>Math.wrap(k++, 10)
=5
>Math.wrap(k++, 10)
=6
>Math.wrap(k++, 10)
=7
>Math.wrap(k++, 10)
=8
>Math.wrap(k++, 10)
=9
>Math.wrap(k++, 10)
=0
>Math.wrap(k++, 10)
=1
>Math.wrap(k++, 10)
=2
>
*/

On a Pico

[espruino-discuss]

Posted at 2018-01-14 by @MaBecker

Have you tried using modulo % instead of Math.wrap()?

[gfwilliams]

Posted at 2018-01-15 by @gfwilliams

Math.wrap doesn't alter the arguments, it just returns a wrapped value.

As such Math.wrap(k++, 10); won't do anything - you'd probably want k=Math.wrap(k+1, 10);

But as @mabe says, for this kind of thing with just integers you could also easily use modulo: k=(k+1)%10;

[espruino-discuss]

Posted at 2018-01-15 by Frida

I just wondered that it was different in a program and in the console.
Because in line 80 it is 9, and in line 82 it is 0.

[gfwilliams]

Posted at 2018-01-15 by @gfwilliams

Maybe I'm misunderstanding... Math.wrap will return a number between 0 and 9, even though at line 80 in the code above, k itself will be somewhere around 40.

In your uploaded code:

  for(var j = 0; j < 30; j++) {
    tmp[i] = i;
    console.log('k = ' + k +'  ' + 'i = ' + i);
    Math.wrap(k++, 10);
    i++; if(i > 9) {i = 0;}
  }

The return value of Math.wrap isn't being used, so you might as well be doing:

  for(var j = 0; j < 30; j++) {
    tmp[i] = i;
    console.log('k = ' + k +'  ' + 'i = ' + i);
    k++;
    i++; if(i > 9) {i = 0;}
  }