Realistic Structured Clone

You might not need this anymore! A native structuredClone function is available in many recent environments, such as Node v17 and Firefox v94. Check if your target environment has structuredClone built in. If it does, use that.

This is a pure JS implementation of the structured clone algorithm (or at least something pretty close to that).

Why do you want this? Well, you probably don't. If your goal is to just clone a JS object, you're better off with lodash's _.cloneDeep or the popular clone module on npm.

Let's try again... why do you want this? If you are making an implementation of an API that explicitly uses the structured clone algorithm (such as IndexedDB), then you want something that handles quirks and edge cases exactly like the structured clone algorithm. That's what realistic-structured-clone is for. It's not totally there (see below) but it's a decent start.

Use

Install through npm:

$ npm install realistic-structured-clone

Then use it:

// First load the module
// (Use Browserify or something if you're targeting the web)
var structuredClone = require('realistic-structured-clone');

// Clone a variable (will throw a DataCloneError for invalid input)
var clonedX = structuredClone(x);

Alternatives

If you look around, you'll notice various modules calling themselves implementations of the structured clone algorithm, such as the structured-clone package on npm. But that package, like all the others I've seen, doesn't actually seem to be an attempt at implementing the structured clone algorithm. It's just some arbitrary type of clone. As I wrote above, this distinction only matters if you really care about the nuances of the structured clone algorithm, which you probably don't.

If you're working in the browser, you can do something like this to do a real structured clone:

function clone(x) {
    return new Promise(function (resolve, reject) {
        window.addEventListener('message', function(e) {
            resolve(e.data);
        });
        window.postMessage(x, "*");
    });
}
var x = {a:[1,2,3], b:{c:1}};
clone(x).then(function(cloned) {
    console.log("x: %s", JSON.stringify(x));
    console.log("cloned: %s", JSON.stringify(cloned));
    console.log("x == cloned %s", x == cloned);
    console.log("x === cloned %s", x === cloned);
});

However, that won't help you in Node.js. It's also asynchronous, which could be a problem. realistic-structured-clone is synchronous and works everywhere.

Current State

As of version 2.0, it should be pretty damn close to the spec! However it is now just a light wrapper around the Typeson structured-cloning-throwing preset.

License

Apache 2.0