Create Posts “using-js-sets-to-find-elements”

content/posts/using-js-sets-to-find-elements.md

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+---
+title: 'Using JS Set''s to Find Elements '
+date: 2019-07-09T20:27:09.247Z
+tags:
+  - Tech
+description: >-
+  JS's `new Set()` can be the new Hash table optimization for reducing nested
+  loops.
+
+
+  https://gitlab.com/snippets/1873655
+---
+Functionally for one check, this is identical to checking the `.indexOf()` or `.includes()` of an Array. However, in cases where you're filtering a large array down to match a list of ID's, for example, the nested looping can result in a performance hit. Traditionally hash tables were used for speeding up this search, but with ES2015 we can now leverage Sets which are easier to read and still result in a single loop that's equal to the length of the Array and no more. (Can be further optimized by ending when running out of needles)
+
+```js
+// Example Data
+let hugeArray = [...Array(10000).keys()].map(id => { return {id}; }); // [{id: 0}, ..., {id: 9999}]
+let needles = [1010, 2020, 3030, 4040, 5050, 6060, 7070, 8080, 9090];
+
+// Finding matching elements
+let needlesSet = new Set(needles);
+let matches = hugeArray.filter(obj => needlesSet.has(obj.id));
+```