fix: node 6 compatibility (#353)

Co-authored-by: ljharb <ljharb@gmail.com>

src/getLuminance.ts

@@ -12,7 +12,7 @@ function getLuminance(color: string): number {
     const channel = x / 255;
     return channel <= 0.03928
       ? channel / 12.92
-      : ((channel + 0.055) / 1.055) ** 2.4;
+      : Math.pow(((channel + 0.055) / 1.055), 2.4);
   }
 
   const [r, g, b] = parseToRgba(color);

src/parseToRgba.ts

@@ -70,9 +70,17 @@ const colorToInt = (x: string) => parseInt(x.replace(/_/g, ''), 36);
 const compressedColorMap = '1q29ehhb 1n09sgk7 1kl1ekf_ _yl4zsno 16z9eiv3 1p29lhp8 _bd9zg04 17u0____ _iw9zhe5 _to73___ _r45e31e _7l6g016 _jh8ouiv _zn3qba8 1jy4zshs 11u87k0u 1ro9yvyo 1aj3xael 1gz9zjz0 _3w8l4xo 1bf1ekf_ _ke3v___ _4rrkb__ 13j776yz _646mbhl _nrjr4__ _le6mbhl 1n37ehkb _m75f91n _qj3bzfz 1939yygw 11i5z6x8 _1k5f8xs 1509441m 15t5lwgf _ae2th1n _tg1ugcv 1lp1ugcv 16e14up_ _h55rw7n _ny9yavn _7a11xb_ 1ih442g9 _pv442g9 1mv16xof 14e6y7tu 1oo9zkds 17d1cisi _4v9y70f _y98m8kc 1019pq0v 12o9zda8 _348j4f4 1et50i2o _8epa8__ _ts6senj 1o350i2o 1mi9eiuo 1259yrp0 1ln80gnw _632xcoy 1cn9zldc _f29edu4 1n490c8q _9f9ziet 1b94vk74 _m49zkct 1kz6s73a 1eu9dtog _q58s1rz 1dy9sjiq __u89jo3 _aj5nkwg _ld89jo3 13h9z6wx _qa9z2ii _l119xgq _bs5arju 1hj4nwk9 1qt4nwk9 1ge6wau6 14j9zlcw 11p1edc_ _ms1zcxe _439shk6 _jt9y70f _754zsow 1la40eju _oq5p___ _x279qkz 1fa5r3rv _yd2d9ip _424tcku _8y1di2_ _zi2uabw _yy7rn9h 12yz980_ __39ljp6 1b59zg0x _n39zfzp 1fy9zest _b33k___ _hp9wq92 1il50hz4 _io472ub _lj9z3eo 19z9ykg0 _8t8iu3a 12b9bl4a 1ak5yw0o _896v4ku _tb8k8lv _s59zi6t _c09ze0p 1lg80oqn 1id9z8wb _238nba5 1kq6wgdi _154zssg _tn3zk49 _da9y6tc 1sg7cv4f _r12jvtt 1gq5fmkz 1cs9rvci _lp9jn1c _xw1tdnb 13f9zje6 16f6973h _vo7ir40 _bt5arjf _rc45e4t _hr4e100 10v4e100 _hc9zke2 _w91egv_ _sj2r1kk 13c87yx8 _vqpds__ _ni8ggk8 _tj9yqfb 1ia2j4r4 _7x9b10u 1fc9ld4j 1eq9zldr _5j9lhpx _ez9zl6o _md61fzm'
   .split(' ')
   .reduce((acc, next) => {
-    acc[colorToInt(next.substring(0, 3))] = colorToInt(next.substring(3))
-      .toString(16)
-      .padStart(6, '0');
+    const key = colorToInt(next.substring(0, 3));
+    const hex = colorToInt(next.substring(3)).toString(16);
+
+    // NOTE: pad start could be used here but it breaks Node 6 compat
+    // https://github.com/ricokahler/color2k/issues/351
+    let prefix = '';
+    for (let i = 0; i < 6 - hex.length; i++) {
+      prefix += '0';
+    }
+
+    acc[key] = `${prefix}${hex}`;
     return acc;
   }, {} as { [key: string]: string });