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C # tutorial
HTML web storage; better than cookies
With web storage, web applications can store data locally within the user's browser.
Before HTML5, application data had to be stored in cookies, included in every server request. Web storage is more secure, and large amounts of data can be stored locally, without affecting website performance.
Unlike cookies, the storage limit is far larger (at least 5MB) and information is never transferred to the server.
Web storage is per origin (per domain and protocol). All pages, from one origin, can store and access the same data.
The numbers in the table specify the first browser version that fully supports Web Storage.
API | |||||
---|---|---|---|---|---|
Web Storage | 4.0 | 8.0 | 3.5 | 4.0 | 11.5 |
HTML web storage provides two objects for storing data on the client:
window.localStorage
- stores data with no expiration datewindow.sessionStorage
- stores data for one session (data is lost when the browser tab is closed)Before using web storage, check browser support for localStorage and sessionStorage:
The localStorage object stores the data with no expiration date. The data will not be deleted when the browser is closed, and will be available the next day, week, or year.
// Store
localStorage.setItem("lastname", "Smith");
// Retrieve
document.getElementById("result").innerHTML = localStorage.getItem("lastname");
Example explained:
The example above could also be written like this:
The syntax for removing the "lastname" localStorage item is as follows:
The following example counts the number of times a user has clicked a button. In this code the value string is converted to a number to be able to increase the counter:
if (localStorage.clickcount) {
localStorage.clickcount = Number(localStorage.clickcount) + 1;
} else {
localStorage.clickcount = 1;
}
document.getElementById("result").innerHTML = "You have clicked the button " +
localStorage.clickcount + " time(s).";
The sessionStorage
object is equal to the localStorage object, except
that it stores the data for only one session. The data is deleted when the user closes the
specific browser tab.
The following example counts the number of times a user has clicked a button, in the current session:
if (sessionStorage.clickcount) {
sessionStorage.clickcount = Number(sessionStorage.clickcount) + 1;
}
else {
sessionStorage.clickcount = 1;
}
document.getElementById("result").innerHTML = "You have clicked the button " +
sessionStorage.clickcount + " time(s) in this session.";