Rename js snippets

snippets/js/s/sum-array.md

@@ -0,0 +1,21 @@
+---
+title: Array sum
+type: snippet
+language: javascript
+tags: [math]
+cover: secret-tree
+dateModified: 2020-10-22T20:24:30+03:00
+---
+
+Calculates the sum of two or more numbers/arrays.
+
+- Use `Array.prototype.reduce()` to add each value to an accumulator, initialized with a value of `0`.
+
+```js
+const sum = (...arr) => [...arr].reduce((acc, val) => acc + val, 0);
+```
+
+```js
+sum(1, 2, 3, 4); // 10
+sum(...[1, 2, 3, 4]); // 10
+```