Workaround for not jet implemented String.padStart/padEnd

[espruino-discuss]

Posted at 2020-09-07 by @MaBecker

Had the need to fill a string with '0' at the end.

var len = 64;   
var sb = parseInt(1023).toString(2);
var sbl = sb.length;
var sbFixedLenStart = ('0').repeat((len-sbl)?(len-sbl):0) + sb;
var sbFixedLenEnd = sb + ('0').repeat((len-sbl)?(len-sbl):0);
console.log(sbFixedLenStart);
console.log(sbFixedLenEnd);

/* output
0000000000000000000000000000000000000000000000000000001111111111
1111111111000000000000000000000000000000000000000000000000000000
*/

[espruino-discuss]

Posted at 2020-09-07 by AkosLukacs

Almost there, but this blows up of the len is smaller than the length of the string without padding. A small modification solves it ((len-sbl>0)):

var len = 6;   
var sb = parseInt(1023).toString(2);
var sbl = sb.length;
var sbFixedLenStart = ('0').repeat((len-sbl>0)?(len-sbl):0) + sb;
var sbFixedLenEnd = sb + ('0').repeat((len-sbl>0)?(len-sbl):0);
console.log(sbFixedLenStart);
console.log(sbFixedLenEnd);

MDN usually has polyfills or in this case, a link to polyfills: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/padStart
Altho might need some tweaks to better fit Espruino's constraints...

[espruino-discuss]

Posted at 2020-09-07 by @MaBecker

Hmm, isn’t a negative value : false?

Edit:

just tested - it is not ........

So many thanks for your input!

[espruino-discuss]

Posted at 2020-09-08 by AkosLukacs

Yepp, JS if full of interesting things, some help:
https://developer.mozilla.org/en-US/docs/Glossary/Truthy
https://developer.mozilla.org/en-US/docs/Glossary/Falsy

Btw

!! 0
> false
!! "0"
> true

Obligatory talk/video: https://www.destroyallsoftware.com/talks/wat

[espruino-discuss]

Posted at 2020-09-08 by @MaBecker

WAT Video is super funny - It is a must - wat a cool guy!

[espruino-discuss]

Posted at 2020-09-08 by @fanoush

!! 0
> false
!! "0"
> true

gives different results which is interesting because

"0"==0
> true

btw tried stuff from wat video in node.js and

> {} + {}
'[object Object][object Object]'

which is not very sophisticated answer, NaN answer was much wiser :-)

[gfwilliams]

Posted at 2020-09-14 by @gfwilliams

Interesting - thanks! If padStart/padEnd really are that simple then they could probably be added to the firmware. It's one of those things that is pretty commonly used

[gfwilliams]

Posted at 2020-10-08 by @gfwilliams

Just added espruino/Espruino@05c89c9