How does the pound sign (#) signal the beginning of a comment in JavaScript?

I recently ran into an issue while trying to minify JavaScript using Grunt in my NPM project. The error thrown by Uglify was:

Warning: Uglification failed.
Unexpected character '#'.
Line 1 in app/min-libs/node_modules/grunt-contrib-jshint/node_modules/jshint/nod
e_modules/cli/examples/cat.js
 Use --force to continue.

Upon investigating the file mentioned in the error, it appears to be from a different NPM module, indicating that the developers are experienced. The line causing the error reads:

#!/usr/bin/env node

This made me wonder if this syntax with '#' is a comment or some kind of secret forbidden technique known only to the owners of this NPM module.

javascriptcommentsnpmjshintuglifyjs2

Answer №1

One interesting fact to note is that this technique does not originate from JavaScript but rather from Unix operating systems. It goes by the name shebang. According to Wikipedia:

When a script with a shebang is executed under Unix-like operating systems, the program loader interprets the rest of the initial line as an instruction for which interpreter program to run instead. This program is then launched, with the path initially used to run the script passed to it as an argument.

Therefore, if you have a file named cat.js, and it has executable permissions, you can simply run it in the shell like an executable.

cat.js

as opposed to

node cat.js

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