walter-whitelist

This lightweight module whitelists javascript objects recursively. This is particularly useful in the following situations:

• you have to check that a user-supplied object only contains keys that the user is allowed to supply, e.g., when handling a POST/PUT request
• you have to pick fields from an object that the user is allowed to see, e.g., before sending a response to a client

Examples

Process user-supplied objects

Before storing user-supplied data in a database, you usually want to check if the object contains fields that the user is allowed to store.

let allowed = {name: true, age: true};
whitelist({name: 'Darth', age: 42}, allowed); // resolves with {name: 'Darth', age: 42}
whitelist({id: 23}, allowed); // rejects with WhitelistError (field 'id' is not allowed)
whitelist({name: 'Darth'}, allowed); // resolves with {name: 'Darth', age: undefined}
// omit keys with undefined values:
whitelist({name: 'Darth'}, allowed, {omitUndefined: true}); // resolves with {name: 'Darth'}

You can also use a function to check fields:

let allowed = {
  name: true,
  age: (age, options) => {
    if (age < 50) return age;
    throw WhitelistError('age must be less than 50', options.path);
  },
};
whitelist({name: 'Darth', age: 42}, allowed); // resolves with {name: 'Darth', age: 42}
whitelist({name: 'Darth', age: 66}, allowed); // rejects with WhitelistError ('age must be less than 50')

Nested objects work, too:

allowed = {name: true, lightsaber: {color: true}};
whitelist({name: 'Darth', lightsaber: {color: 'red'}}, allowed);  // resolves with {name: 'Darth', lightsaber: {color: 'red'}}
whitelist({name: 'Darth'}, allowed);  // resolves with {name: 'Darth', lightsaber: {color: undefined}}
// omit keys with undefined values:
whitelist({name: 'Darth'}, allowed, {omitUndefined: true}); // resolves with {name: 'Darth', lightsaber: {}}

Pick allowed fields

Before sending data from a database to a client, you want to pick only fields that the client is allowed to see. This can be achieved by using the option omitDisallowed: true.

let allowed = {name: true, age: true};
whitelist({id: 23, name: 'Darth', age: 42}, allowed, {omitDisallowed: true}); // resolves with {name: 'Darth', age: 42}
whitelist({id: 23, name: 'Darth'}, allowed, {omitDisallowed: true}); // resolves with {name: 'Darth', age: undefined}
// omitDisallowed can be combined with omitUndefined:
whitelist({id: 23, name: 'Darth'}, allowed,
  {omitDisallowed: true, omitUndefined: true}); // resolves with {name: 'Darth'}

Installation

npm install walter-whitelist

Documentation

const whitelist = require('walter-whitelist');

whitelist(src, allowed, options)

• src: source object, array or primitive
• allowed: the checks on src are performed according to this value. The following values are accepted:
  • an object {key: value, ...}:
    • expects src to be an object.
    • iterates over keys and uses the value for whitelisting the corresponding key/value pair in src
    • value can be any value that is accepted as the allowed parameter
  • an array with one element [value]:
    • expects src to be an array
    • iterates over elements of array src and whitelists according to value
    • value can be any value that is accepted as the allowed parameter
  • a function fn(src, options):
    • should return the whitelisted src (directly or via a promise)
    • if omitDisallowed is false and src contains disallowed data, the function is responsible for throwing a WhitelistError (or rejecting the returned promise with a WhitelistError)
  • a boolean: if the value is true, src is allowed and returned as the result
• options: an object with the following optional keys:
  • omitUndefined: if set to true, it omits fields in the result whose values are undefined
  • omitDisallowed: if set to true, it omits fields from src that are not present in allowed.
  • data: custom data that is recursively passed to any function in the allowed parameter.

The function returns a new object with the whitelisted fields and throws a whitelist.WhitelistError if a field in src is not allowed (unless omitDisallow is true).