$ npm install shebang-regex

const shebangRegex = require('shebang-regex');

const string = '#!/usr/bin/env node\nconsole.log("unicorns");';

shebangRegex.test(string);
//=> true

shebangRegex.exec(string)[0];
//=> '#!/usr/bin/env node'

shebangRegex.exec(string)[1];
//=> '/usr/bin/env node'