Pad a given number with leading zeroes. Useful to make it a fixed width like with e.g. sprintf in other programming langages.
00001, 00012, 00123, 01234, 12345pad(number, count);
// returns number with leading zerosSee the 140byt.es site for a showcase of entries (built itself using 140-byte entries!), and follow @140bytes on Twitter. And check my "JavaScript Golf Lessons" slides.
| function( | |
| a, // the number to convert | |
| b // number of resulting characters | |
| ){ | |
| return ( | |
| [ 1e15 ] + a // combine with large number | |
| ).slice(-b) // cut leading "1" | |
| } |
| function(a,b){return([1e15]+a).slice(-b)} |
| DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE | |
| Version 2, December 2004 | |
| Copyright (C) 2011 YOUR_NAME_HERE <YOUR_URL_HERE> | |
| Everyone is permitted to copy and distribute verbatim or modified | |
| copies of this license document, and changing it is allowed as long | |
| as the name is changed. | |
| DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE | |
| TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION | |
| 0. You just DO WHAT THE FUCK YOU WANT TO. |
| { | |
| "name": "pad", | |
| "description": "Pad a given number with leading zeroes.", | |
| "contributors": [ | |
| "aemkei", | |
| "tsaniel", | |
| "jed" | |
| ], | |
| "keywords": [ | |
| "number", | |
| "format" | |
| ] | |
| } |
| <!DOCTYPE html> | |
| <title>Leading Zeros</title> | |
| <pre id="output"></pre> | |
| <script> | |
| for (var i=10; i--;){ | |
| function pad(a,b){return([1e15]+a).slice(-b)} | |
| document.getElementById("output").innerHTML += pad( | |
| Math.pow(3, i+1), 5 | |
| ) + "\n"; | |
| } | |
| </script> |
Nice: This saved 5 chars, so we are now at 49 bytes!
function(a,b){return(a+1e15+"").slice(-b)}(42 bytes, and no eval)
JEDは、先生です！If we limit the count to 9 it would save an extra byte a+1e9+"" - but 15 places are more flexible.
BTW: Why does it not work with 1e16?
1e16 + 3 === 10000000000000004Can you point me to some resources with all the JS math limit stuff?
to be honest, it's not my forte. i defer to the REAL sensei, like peter van der zee and mathias bynens. i'm more of a pragmatist, and just worked my way down until it did what i wanted it to.
I don't know much, but i believe it's because JavaScript uses the "double-precision 64-bit binary format IEEE 754 value" to repersent numbers, and it always causes such a problem.
Another typical problem:
0.1 + 0.2 = 0.30000000000000004
http://es5.github.com/#x8.5
Yep, that's the reason.
Inspired by @LeverOne's trick, we can save another byte.
function(a,b){return([1e15]+a).slice(-b)}
nice one, @tsaniel. funny how the logic is also completely different: you took out all the math!
Now down to 41 bytes, guys. - And I love the evolution of the original code!
It might be good to highlight the limitations of this approach.
if a > 20 characters you run into scientific notation problems ([ 1e15 ] + 1234567891012345678901) = "10000000000000001.2345678910123457e+21"
if b is shorter than a your number will be truncated.
Change substr to slice and save 1 byte.
Also change Math.pow(10,count) to eval('1e'+count), and the placing of coercion.
function(a,b){return(eval('1e'+b)+a+'').slice(1)}