Copy to clipboard in Node.js?

Check out clipboardy. It lets you copy/paste cross-platform. It is more actively maintained than the copy-paste module mentioned in another answer and it fixes many of that module's issues.

const clipboardy = require('clipboardy');

// Copy
clipboardy.writeSync('🦄');

// Paste
clipboardy.readSync();
//🦄

For OS X:

function pbcopy(data) {
    var proc = require('child_process').spawn('pbcopy'); 
    proc.stdin.write(data); proc.stdin.end();
}

write() can take a buffer or a string. The default encoding for a string will be utf-8.