Terminal window becomes busy

Hi,
I am trying below sample code on my MAC
`
#!/usr/bin/env node

const vorpal = require('vorpal')();

vorpal
.command('say [words...]')
.option('-b, --backwards')
.option('-t, --twice')
.action(function (args, callback) {
let str = args.words.join(' ');
str = (args.options.backwards) ?
str.split('').reverse().join('') :
str;
this.log(str);
callback();
});

vorpal.show();`

after that I did **npm link** to set it in global,

when I executed js-cli the terminal window becomes busy,