# devalue
Like `JSON.stringify`, but handles
* cyclical references (`obj.self = obj`)
* repeated references (`[value, value]`)
* `undefined`, `Infinity`, `NaN`, `-0`
* regular expressions
* dates
* `Map` and `Set`
Try it out on [runkit.com](https://npm.runkit.com/devalue).
## Goals:
* Performance
* Security (see [XSS mitigation](#xss-mitigation))
* Compact output
## Non-goals:
* Human-readable output
* Stringifying functions or non-POJOs
## Usage
```js
import devalue from '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: ``;
```
Which would result in this:
```html
```
Using `devalue`, we're protected against that attack:
```js
const template = `
`;
```
```html
```
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
* [jsesc](https://github.com/mathiasbynens/jsesc) by Mathias Bynens
## License
[MIT](LICENSE)