I want to add task in my project but i am unable to add Node.js

[Phil_Seeman]

No, you can only assign a task to one user. This is a limitation of Asana which is a design decision on their part; you can read about that decision here:

Why one assignee?

If you want to register your vote that you’d like to have that changed, you can do so here:

Assign multiple assignees on one task

There are cases when adding more than one person to a task as assignee would be very handy.