JavaScript has a variety of built-in popup APIs that display special UI for user interaction. Famously:
alert("Hello, World!");The UI for this varies from browser to browser, but generally you’ll see a little window pop up front and center in a very show-stopping way that contains the message you just passed. Here’s Firefox and Chrome:
There is one big problem you should know about up front
JavaScript popups are blocking.
The entire page essentially stops when a popup is open. You can’t interact with anything on the page while one is open — that’s kind of the point of a “modal” but it’s still a UX consideration you should be keenly aware of. And crucially, no other main-thread JavaScript is running while the popup is open, which could (and probably is) unnecessarily preventing your site from doing things it needs to do.
Nine times out of ten, you’d be better off architecting things so that you don’t have to use such heavy-handed stop-everything behavior. Native JavaScript alerts are also implemented by browsers in such a way that you have zero design control. You can’t control *where* they appear on the page or what they look like when they get there. Unless you absolutely need the complete blocking nature of them, it’s almost always better to use a custom user interface that you can design to tailor the experience for the user.
With that out of the way, let’s look at each one of the native popups.
window.alert();
window.alert("Hello World");
const button = document.querySelectorAll("button");
button.addEventListener("click", () => {
alert("Text of button: " button.innerText);
});
See the Pen
alert(“Example”); by Elliot KG (@ElliotKG)
on CodePen.
What it’s for: Displaying a simple message or debugging the value of a variable.
How it works: This function takes a string and presents it to the user in a popup with a button with an “OK” label. You can only change the message and not any other aspect, like what the button says.
The Alternative: Like the other alerts, if you have to present a message to the user, it’s probably better to do it in a way that’s tailor-made for what you’re trying to do.
If you’re trying to debug the value of a variable, consider console.log("`Value of variable:"`, variable); and looking in the console.
window.confirm();
window.confirm("Are you sure?");
let answer = window.confirm("Do you like cats?");
if (answer) {
// User clicked OK
} else {
// User clicked Cancel
}
See the Pen
confirm("Example"); by Elliot KG (@ElliotKG)
on CodePen.
What it’s for: “Are you sure?”-style messages to see if the user really wants to complete the action they’ve initiated.
How it works: You can provide a custom message and popup will give you the option of “OK” or “Cancel,” a value you can then use to see what was returned.
The Alternative: This is a very intrusive way to prompt the user. As Aza Raskin puts it:
...maybe you don’t want to use a warning at all.”
There are any number of ways to ask a user to confirm something. Probably a clear UI with a wired up to do what you need it to do.
window.prompt();
window.prompt("What’s your name?");
let answer = window.prompt("What is your favorite color?");
// answer is what the user typed in, if anything
See the Pen
prompt("Example?", "Default Example"); by Elliot KG (@ElliotKG)
on CodePen.
What it’s for: Prompting the user for an input. You provide a string (probably formatted like a question) and the user sees a popup with that string, an input they can type into, and “OK” and “Cancel” buttons.
How it works: If the user clicks OK, you’ll get what they entered into the input. If they enter nothing and click OK, you’ll get an empty string. If they choose Cancel, the return value will be null.
The Alternative: Like all of the other native JavaScript alerts, this doesn’t allow you to style or position the alert box. It’s probably better to use a