User Prompts are methods part of the Web Application API used to invoke Browser modals requesting a user action such as confirmation or input.
Show a modal popup with a message to the user.
Requires the user to click [OK] to dismiss.
More information below in "Using alert()".
boolean = window.confirm(message)
Show a modal popup with the provided message.
Provides [OK] and [Cancel] buttons which will respond with a boolean value true / false respectively.
Show a modal popup with the provided message and an input field with an optional pre-filled value.
Returns as result the user provided input value.
Opens a modal with document print options
Persistent Prompt Modal
When using prompt a user can always click Cancel and no value will be returned.
To prevent empty values and make it more persistent:
Confirm to Delete element
A way to use confirm() is when some UI action does some destructive changes to the page and is better accompanied by a notification and a user confirmation - like i.e. before deleting a post message:
Usage of alert()
The alert() method of the window object displays an alert box with a specified message and an OK or Cancel button. The text of that button depends on the browser and can't be modified.
An alert box is often used if you want to make sure information comes through to the user.
Usage of prompt()
Prompt will display a dialog to the user requesting their input. You can provide a message that will be placed above the text field. The return value is a string representing the input provided by the user.
You can also pass prompt() a second parameter, which will be displayed as the default text in the prompt's text field.