Question
I'd like to store a JavaScript object in HTML5 localStorage
, but my object
is apparently being converted to a string.
I can store and retrieve primitive JavaScript types and arrays using
localStorage
, but objects don't seem to work. Should they?
Here's my code:
var testObject = { 'one': 1, 'two': 2, 'three': 3 };
console.log('typeof testObject: ' + typeof testObject);
console.log('testObject properties:');
for (var prop in testObject) {
console.log(' ' + prop + ': ' + testObject[prop]);
}
// Put the object into storage
localStorage.setItem('testObject', testObject);
// Retrieve the object from storage
var retrievedObject = localStorage.getItem('testObject');
console.log('typeof retrievedObject: ' + typeof retrievedObject);
console.log('Value of retrievedObject: ' + retrievedObject);
The console output is
typeof testObject: object
testObject properties:
one: 1
two: 2
three: 3
typeof retrievedObject: string
Value of retrievedObject: [object Object]
It looks to me like the setItem
method is converting the input to a string
before storing it.
I see this behavior in Safari, Chrome, and Firefox, so I assume it's my misunderstanding of the HTML5 Web Storage specification, not a browser-specific bug or limitation.
I've tried to make sense of the structured clone algorithm described in 2 Common infrastructure. I don't fully understand what it's saying, but maybe my problem has to do with my object's properties not being enumerable (???).
Is there an easy workaround?
Update: The W3C eventually changed their minds about the structured-clone specification, and decided to change the spec to match the implementations. See 12111 – spec for Storage object getItem(key) method does not match implementation behavior. So this question is no longer 100% valid, but the answers still may be of interest.
Answer
Looking at the [Apple](https://developer.apple.com/library/archive/documentation/iPhone/Conceptual/SafariJSDatabaseGuide/Name- ValueStorage/Name-ValueStorage.html), Mozilla and [Mozilla again](https://developer.mozilla.org/en- US/docs/Web/API/Storage/setItem) documentation, the functionality seems to be limited to handle only string key/value pairs.
A workaround can be to stringify your object before storing it, and later parse it when you retrieve it:
var testObject = { 'one': 1, 'two': 2, 'three': 3 };
// Put the object into storage
localStorage.setItem('testObject', JSON.stringify(testObject));
// Retrieve the object from storage
var retrievedObject = localStorage.getItem('testObject');
console.log('retrievedObject: ', JSON.parse(retrievedObject));