Javascript to show alert with input box

Hello All,

I want to show a popup to user with input field.

Example. If user clicks on 'UpdateRelationship' button available on 'Account' form, a pop up should open with input box which allows user to enter the name of the relationship. Once user enters the name and clicks Ok button, the name of relationship should be updated in the entity.

I was thinking about showmodaldialog or Xrm.Internal.openDialog, but these methods seems to be an unsupported. i also have tried alert.js library, but there is no provision to take the input from the user.

I'm using CRM 365 online version.

Please tell me how we can show a popup with input box to user.