adds util to chedk scroll direction

README.md

@@ -171,6 +171,7 @@ Located in `src/utils/`.
 // Usage
 import example from "$utils/example.js";
 ```
+* `checkScrollDir.js`: Gets the user's scroll direction ("up" or "down")
 * `csvDownload.js`: Converts a flat array of data to CSV content ready to be used as an `href` value for download.
 * `generateId.js`: Generate an alphanumeric id.
 * `loadCsv.js`: Loads and parses a CSV file.

src/utils/checkScrollDir.js

@@ -0,0 +1,24 @@
+/* Usage
+<script>
+import checkScrollDir from "$utils/checkScrollDir.js";
+let scrollY;
+$: scrollDir = checkScrollDir(scrollY);
+$: console.log(scrollDir)
+</script>
+
+<svelte:window bind:scrollY={scrollY} />
+*/
+
+let prevY = 0;
+let scrollDir;
+
+export default function checkScrollDir(scrollY) {
+    if (scrollY) {
+        scrollDir = scrollY > prevY ? "down" : "up";
+        prevY = scrollY;
+        return scrollDir;
+    } else {
+        scrollDir = undefined;
+        return scrollDir;
+    }
+}