1
0
Fork 0
mirror of https://github.com/denoland/deno.git synced 2024-12-25 08:39:09 -05:00
denoland-deno/std/node/tests/node_modules/left-pad/index.js

52 lines
1.4 KiB
JavaScript

/* This program is free software. It comes without any warranty, to
* the extent permitted by applicable law. You can redistribute it
* and/or modify it under the terms of the Do What The Fuck You Want
* To Public License, Version 2, as published by Sam Hocevar. See
* http://www.wtfpl.net/ for more details. */
"use strict";
module.exports = leftPad;
var cache = [
"",
" ",
" ",
" ",
" ",
" ",
" ",
" ",
" ",
" "
];
function leftPad(str, len, ch) {
// convert `str` to a `string`
str = str + "";
// `len` is the `pad`'s length now
len = len - str.length;
// doesn't need to pad
if (len <= 0) return str;
// `ch` defaults to `' '`
if (!ch && ch !== 0) ch = " ";
// convert `ch` to a `string` cuz it could be a number
ch = ch + "";
// cache common use cases
if (ch === " " && len < 10) return cache[len] + str;
// `pad` starts with an empty string
var pad = "";
// loop
while (true) {
// add `ch` to `pad` if `len` is odd
if (len & 1) pad += ch;
// divide `len` by 2, ditch the remainder
len >>= 1;
// "double" the `ch` so this operation count grows logarithmically on `len`
// each time `ch` is "doubled", the `len` would need to be "doubled" too
// similar to finding a value in binary search tree, hence O(log(n))
if (len) ch += ch;
// `len` is 0, exit the loop
else break;
}
// pad `str`!
return pad + str;
}