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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   spec, not a browser-specific bug or limitation.

I've tried to make sense of the structured clone algorithm described in http://www.w3.org/TR/html5/infrastructure.html 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 https://www.w3.org/Bugs/Public/show_bug.cgi?id=12111.So this question is no longer 100% valid, but the answers still may be of interest.

1 Answer

0 votes
by (40.3k points)

In AppleMozillaand Mozilla again documentation, the functionalities are 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));

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