# 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)