Storage.setItem()
 The setItem() method of the Storage interface, when passed a key name and value, will add that key to the given Storage object, or update that key's value if it already exists. 
Syntax
storage.setItem(keyName, keyValue);
Parameters
keyName-  
A
DOMStringcontaining the name of the key you want to create/update. keyValue-  
A
DOMStringcontaining the value you want to give the key you are creating/updating. 
Return value
Exceptions
 setItem() may throw an exception if the storage is full. Particularly, in Mobile Safari (since iOS 5) it always throws when the user enters private mode. (Safari sets the quota to 0 bytes in private mode, unlike other browsers, which allow storage in private mode using separate data containers.) Hence developers should make sure to setItem(). 
Example
The following function creates three data items inside local storage.
function populateStorage() { localStorage.setItem('bgcolor', 'red'); localStorage.setItem('font', 'Helvetica'); localStorage.setItem('image', 'myCat.png'); }
Note: To see this used within a real world example, see our Web Storage Demo.
Specifications
| Specification | 
|---|
| HTML Standard (HTML) # dom-storage-setitem-dev  | 
Browser compatibility
| Desktop | Mobile | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | |
setItem | 
4  | 
12  | 
3.5  | 
8  | 
10.5  | 
4  | 
≤37  | 
18  | 
6  | 
11  | 
3.2  | 
1.0  | 
See also
    © 2005–2021 MDN contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
    https://developer.mozilla.org/en-US/docs/Web/API/Storage/setItem