Add orderByEnum snippet

snippets/orderByEnum.md

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+---
+title: orderByEnum
+tags: array,intermediate
+---
+
+Returns a sorted array of objects ordered by a property, which has a known set of values (enum).
+The desired order is defined by the given `order` array.
+
+- Uses the `order` array's `indexOf` method to find the desired order for the respective value.
+- Uses the difference of both indices to determine the order, as any negative or positive number suffices (not just `-1` or `1`). 
+- Throws an error if the property has an unknown value.
+
+```js
+const orderByEnum = (arr, prop, order) =>
+  [...arr].sort((a, b) => {
+    const aOrderIndex = order.indexOf(a[prop]), bOrderIndex = order.indexOf(b[prop]);
+    if (aOrderIndex === -1) {
+      throw new Error(`Unexpected value ${a[prop]}`)
+    }
+    if (bOrderIndex === -1) {
+      throw new Error(`Unexpected value ${b[prop]}`)
+    }
+    return aOrderIndex - bOrderIndex;
+  });
+```
+
+```js
+const users = [{ name: 'fred', language: 'Javascript' }, { name: 'barney', language: 'TypeScript' }, { name: 'frannie', language: 'Javascript' }, { name: 'anna', language: 'Java' }]
+orderByEnum(users, 'language', ['Javascript', 'TypeScript', 'Java'])
+// [{name: "fred", language: "Javascript"}, {name: "frannie", language: "Javascript"}, {name: "barney", language: "TypeScript"}, {name: "anna", language: "Java"}]
+```