jamiebuilds / guarded-string

Prevent accidentally introducing XSS holes with the strings in your app

guarded`string`

Prevent accidentally introducing XSS holes with the strings in your app

Hold your friends close, and your strings closer

Installation

yarn add guarded-string

Usage

Important! This should be used for things like preventing XSS attacks, not for hiding sensitive information.

import guardedString from 'guarded-string';

const myString = guardedString`My very important (but not too important) string`;

guardedString.isGuarded(myString); // >> boolean
guardedString.assertGuarded(myString); // >> maybe throws
guardedString.toUnguarded(myString); // >> unguarded string (throws on other value types)

myString + ''; // 'My very important (but not too important) string'

guardedString.freeze(myString);
guardedString.isFrozen(myString);
guardedString.assertFrozen(myString);

myString + ''; // Error!
JSON.stringify(myString); // Error!
// etc.

API

guardedString

Create a guarded string. This must be used as a tagged template literal with no interpolations. You cannot construct a guarded string that is not statically written in your code.

let str = guardedString`Hello World`;

You can continue using this as a string, but when you modify it, the result is an unguarded (regular) string.

let str1 = guardedString`Hello World`;
let str2 = str1 + '!';

guardedString.isGuarded(str1); // true
guardedString.isGuarded(str2); // false

If you want to using string methods, you can wrap your string with String(str) or guardedString.toUnguarded(str).

let str1 = guardedString`Hello World`;
let str2 = String(str1).replace('World', 'Universe');
let str3 = guardedString.toUnguarded(str1).replace('World', 'Universe');

guardedString.isGuarded(val)

This just returns a boolean if the value you pass in is a guarded string or not.

guardedString.assertGuarded(val)

This will throw an error if the value you pass in is not a guarded string.

guardedString.freeze(str)

If you want to make sure that your string is not accidentally stringified, you can call guardedString.freeze(str) on your guarded string and it will prevent code from accidentally stringifying it.

let str = guardedString.freeze(guardedString`Hello World`);

String(str); // Error!
str + '!'; // Error!
JSON.stringify(str); // Error!

See test cases for more

Note that you can still call guardedString.toUnguarded(str) to convert it back to a plain string.

guardedString.isFrozen(val)

This just returns a boolean if the value you pass in is a frozen string or not.

guardedString.assertFrozen(val)

This will throw an error if the value you pass in is not a frozen string.

guardedString.toUnguarded(str)

This will convert any guarded string (including frozen strings).

let str1 = guardedString.freeze(guardedString`Hello World`);
let str2 = guardedString.toUnguarded(str1);

console.log(typeof str1); // 'object'
console.log(typeof str2); // 'string'