Generating a regular expression to match valid JavaScript identifiers

View the source code to see how it’s done exactly. (A Node.js version of this script is also available.) This page combines the following resources and tools:

• Write-up: valid JavaScript variable names in ES6.
• Write-up: valid JavaScript variable names in ES5.
• Write-up: reserved keywords in ECMAScript 5 and in ECMAScript 6.
• Regenerate, a JavaScript library to easily generate regular expressions based on a set of symbols or code points.
• The unicode-data project and its HTTP API are used to get the list of symbols and code points in the relevant Unicode categories as per Unicode v8.0.0.

Note that the generated regular expressions don’t account for Unicode escape sequences in the identifier, so be sure to unescape those before validating.

Fun fact: comparing the output for ES 5.1 and ES 6 exposed a potential compatibility hazard.

ECMAScript 5.1 / Unicode v8.0.0 generate regex

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ECMAScript 6 / Unicode v8.0.0 generate regex

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