Prompt, Alert, Confirm

Javascript's Input/Output functions.


Javascript provides a simple way to collect input from the user - the prompt() function:

// Input must be stored in a variable or else it goes nowhere!
let userResponse = prompt("What is your name?");

The prompt command has two arguments. prompt(text, [defaultText]) and returns a string of what the user entered. It is important to note, that it returns a string.

If the user clicks cancel, then the prompt() function returns null.


The console is a great way to give output as a developer (testing, errors, warnings) but general users do not see the console window! If you want to give a quick pop-up of information to the user (without any input from the user), you can use the alert() function.

The alert() function is very simple. It takes a string and returns nothing. To use it, you just call it with whatever you want shown in the pop-up box.

alert("The sky is falling, the sky is falling!");


Maybe you don't want text from the user but rather a YES or NO (or perhaps OK or CANCEL). Javascript provides the confirm() function to ask the user a question and present them with two choices that equate to true or false.

The ability to retrieve a boolean value from the user can be very useful. The confirm() function takes a string as input and returns a boolean.

let userAnswer = confirm("You will become a zombie");

While many examples could be provided of the three methods listed, it is much more rewarding if you try them out yourself.

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