Trick to add all friends to facebook group by a single click:

Method 1: Add all friends to facebook group script:

First, click on Create group and write a group name.

Note:

• Select only one friend in Members section to initiate all group related processes.
• Privacy of Group:
  Facebook takes care of your group members privacy. So you have to choose a privacy option which your group wants.
• Here some other instructions for facebook group permissions:
  Public:
  Anyone can see the group, its members, and their posts.
  Closed:
  Anyone can find the group and see who is a member of it, but only members can see posts.
  Secret:
  Only members can find the group and see posts.

• Now click on create a group then choose an icon of your group and click on OK.
• You have created a group. Now, add some description about your group and click on add members section box.
• Copy a given code from this link

Metod 2 use https://chrome.google.com/webstore/detail/group-invite-all/eeajicmampllnpkmfimkhefbndkfeloo