Browser APIs

Storing and retrieving string-based data in the browser.

Term / Syntax	Name	Description	Example
localStorage.setItem()	Store Persistent Value	Stores a string value under a specified key and keeps it across browser sessions.	localStorage.setItem("theme", "dark");
localStorage.getItem()	Read Persistent Value	Returns the value stored under a specified key, or null if the key does not exist.	const theme = localStorage.getItem("theme");
localStorage.removeItem()	Remove Persistent Value	Removes the value stored under a specified key.	localStorage.removeItem("theme");
localStorage.clear()	Clear Persistent Storage	Removes all values stored in local storage for the current origin.	localStorage.clear();
sessionStorage.setItem()	Store Session Value	Stores a string value for the current page session.	sessionStorage.setItem("step", "2");
sessionStorage.getItem()	Read Session Value	Returns a session value stored under a specified key, or null if the key does not exist.	const step = sessionStorage.getItem("step");
sessionStorage.removeItem()	Remove Session Value	Removes the value stored under a specified key for the current page session.	sessionStorage.removeItem("step");
JSON.stringify() + localStorage	Store Structured Data	Converts a JavaScript value to JSON text before storing it in local storage.	localStorage.setItem("user", JSON.stringify(user));
JSON.parse() + localStorage	Read Structured Data	Parses stored JSON text back into a JavaScript value.	const user = JSON.parse(localStorage.getItem("user"));

Scheduling code to run after a delay or repeatedly at a specified interval.

Term / Syntax	Name	Description	Example
setTimeout()	Delayed Execution	Schedules a function to run once after at least the specified delay in milliseconds.	setTimeout(showMessage, 1000);
clearTimeout()	Cancel Timeout	Cancels a timeout before its scheduled function runs.	clearTimeout(timeoutId);
setInterval()	Repeated Execution	Schedules a function to run repeatedly with approximately the specified delay between executions.	const intervalId = setInterval(updateClock, 1000);
clearInterval()	Cancel Interval	Stops a repeating interval created with setInterval().	clearInterval(intervalId);

Reading the current URL and controlling browser navigation from JavaScript.

Term / Syntax	Name	Description	Example
window.location.href	Current URL	Returns the current page URL or navigates to a new URL when assigned a value.	window.location.href = "/about.html";
window.location.reload()	Reload Page	Reloads the current page.	window.location.reload();
window.location.assign()	Navigate to URL	Navigates to a specified URL and keeps the current page in the browser's session history.	window.location.assign("/about.html");
window.location.replace()	Replace Current Page	Navigates to a specified URL while replacing the current page in the browser's session history.	window.location.replace("/login.html");

Reading common information provided by the browser and current viewport.

Term / Syntax	Name	Description	Example
window.innerWidth	Viewport Width	Returns the width of the browser's layout viewport in CSS pixels.	const width = window.innerWidth;
window.innerHeight	Viewport Height	Returns the height of the browser's layout viewport in CSS pixels.	const height = window.innerHeight;
navigator.language	Preferred Language	Returns the user's preferred browser language as a language tag.	const language = navigator.language;
navigator.onLine	Online Status	Indicates whether the browser reports that a network connection is available.	if (navigator.onLine) { /* connected */ }