Performance measuring, scroll to top, array flattening

snippets/flatten-array.md

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+### Flatten array
+
+Use recursion.
+Use `reduce()` to get all elements that are not arrays, flatten each element that is an array.
+
+```js
+var flatten = arr =>
+  arr.reduce( (a, v) => a.concat( Array.isArray(v) ? flatten(v) : v ), []);
+```

snippets/measure-time-taken-by-function.md

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+### Measure time taken by function
+
+Use `performance.now()` to get start and end time for the function, `console.log()` the time taken.
+First argument is the function name, subsequent arguments are passed to the function.
+
+```js
+var timeTaken = (f,...args) => {
+  var t0 = performance.now(), r = f(...args);
+  console.log({performance.now() - t0);
+  return r;
+}
+```

snippets/scroll-to-top.md

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+### Scroll to top
+
+Get distance from top using `document.documentElement.scrollTop` or `document.body.scrollTop`.
+Scroll by a fraction of the distance from top. Use `window.requestFrame()` to animate the scrolling.
+
+```js
+var scrollToTop = _ => {
+  var c = document.documentElement.scrollTop || document.body.scrollTop;
+  if(c > 0) {
+    window.requestAnimationFrame(scrollToTop);
+    window.scrollTo(0, c - c/8);
+  }
+}
+```