In a browser, window is the object for the current tab. It is the global object, so alert("Saved") and window.alert("Saved") call the same function. window.document is the page. window.location is the URL.
Some members are properties you read: innerWidth, closed, location.href. Others are methods you call: alert(), setTimeout(), open(). setTimeout returns a number in the browser. Pass that number to clearTimeout if you need to cancel the timer.
This page teaches what window is. The Window Methods index and Window Properties index list every method guide and property in this JavaScript tutorial.
window.innerWidth is a number. window.alert("Saved") is a function call. window.innerWidth() throws.
Common ways to use the window in a browser script:
window.alert("Saved"); // method, returns undefined
const id = window.setTimeout(fn, 1000);
window.clearTimeout(id);
const url = window.location.href; // property, a string
const wide = window.innerWidth; // property, a number
const same = window === window.self;Ideas every JavaScript window tutorial builds on:
| Idea | Example | Remember |
|---|---|---|
| Global | window === self | The tab is the global object |
| Page | window.document | The DOM lives on document |
| URL | location.href | A string, no parentheses |
| Size | innerWidth | Viewport width in CSS pixels |
| Dialog | alert("Saved") | Blocks until OK, returns undefined |
| Timer | setTimeout(fn, 1000) | Returns an id you can cancel |
Three short browser programs. The output is what those lines print in a tab.
self is this window. alert is a function on it.
console.log(typeof window);
console.log(window === window.self);
console.log(typeof window.alert);"object" in a browser tab.true."function".The URL is a string. The viewport width is a number. This page is still open.
console.log(typeof window.location.href);
console.log(typeof window.innerWidth);
console.log(window.closed);"string"."number".false while this tab is still open.Schedule a log, then cancel it before it runs. The delayed line never prints.
const id = window.setTimeout(function () {
console.log("later");
}, 1000);
console.log(typeof id);
window.clearTimeout(id);
console.log("canceled");"later" and, in the browser, returns a numeric id."later" is not printed.canceled immediately.After you know what the window is, open the indexes for the rest of this JavaScript tutorial.
| Look up | Why |
|---|---|
alert() | Show a message and wait for OK |
setTimeout() | Run a function once after a delay |
open() | Open another tab and keep a reference |
innerWidth | Read the viewport width |
Full lists: Window Methods index and Window Properties index.
Open the index for alert(), setTimeout(), open(), and the rest.
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