/bin/su in node.js

When I run

su = spawn '/bin/echo', ['user']
su.stdout.on 'data', (data) ->
    console.log data.toString()

it will correctly write user on console. But When I run

su = spawn '/bin/su', ['user']
su.stdout.on 'data', (data) ->
    console.log data.toString()

it will never end. Is it fixable?