add lighten snippet

snippets/lighten.md

@@ -0,0 +1,28 @@
+---
+title: lighten
+tags: string,browser,regexp,beginner
+---
+
+Returns the string value for the lightened color in `hsl` format.
+
+- Use `String.prototype.match()` to get an array of 3 string with the numeric values.
+- Use `Array.prototype.map()` in combination with `Number` to convert them into an array of numeric values.
+- Clamp new lightness within the hsl valid range between `0` and `100`.
+- Form a valid `hsl` color string.
+
+```js
+const lighten = (amount, hslStr) => {
+  const [hue, saturation, lightness] = hslStr.match(/\d+/g).map(Number);
+
+  const newLightness = Math.max(
+    0,
+    Math.min(100, lightness + parseFloat(amount))
+  );
+
+  return `hsl(${hue}, ${saturation}%, ${newLightness}%)`;
+};
+```
+
+```js
+lighten(10, "hsl(330, 50%, 50%)"); // 'hsl(330, 50%, 60%)'
+```