Add numeric-separators til

Author: bpugh

javascript/numeric-separators.md

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+---
+date: 2024-07-02
+---
+
+# Numeric separators
+
+Today I learned about [numeric separators](https://v8.dev/features/numeric-separators) in javascript.
+They are a small bit of syntactic sugar to make large numeric literals easier to read by letting you insert underscores anywhere in the number.
+
+For example, if you need to specify 10mb in byes, instead of `10485760`, you can write it as:
+
+```js
+const maxUploadSize = 10_485_760;
+```
+
+They were added in ECMAScript 2021 and in C# 7.