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data-guardian 🔒

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data-guardian is a nimble, zero-dependency and lightweight NPM package crafted for developers who prioritize data security and privacy. This handy utility enables you to mask sensitive strings and object properties, safeguarding critical data from prying eyes, especially in logs or UI displays. Notably, it maintains the immutability of your data by default, though this feature is optional and customizable based on your needs.

✨ Features

  • 🔒 String Masking: Conceal parts of a string to hide sensitive data while keeping some characters visible for validation.
  • 🕵️ Object Masking: Automatically masks properties identified as sensitive in objects.
  • 📜 Argument Masking: Mask sensitive data in an array of arguments.
  • 📝 Custom Sensitive Data: Define your own custom regular expressions to identify and mask sensitive data in strings.
  • 🗃️ Collection Masking: Automatically mask sensitive data in Map, Set, and Error instances.
  • 🔮 Immutability (Optional): By default, it doesn't alter your original data structure unless configured to do so.
  • 🖌️ Custom Masking: Define your custom logic to pinpoint which keys in objects should be masked.
  • 📦 Lightweight: No dependencies, no bloat. data-guardian is a lightweight package that won't slow down your app.
  • ⚙️ Configurable: Set the masking character to any commonly used character, and specify the length of the content to mask.
  • 🕵️ Fixed length masking: Ability to mask a fixed length of characters in a string. This removes hints of actual length of the sensitive data.
  • 📚 Typescript Support: data-guardian is written in TypeScript and comes with full type definitions.
  • 📜 Explicit exclusion for masking: Explicitly exclude potential sensitive content in strings by wrapping the content with '##'

🚀 Getting Started


npm install data-guardian


Here's a quick peek at how data-guardian can be integrated into your JavaScript/TypeScript projects:

const { maskData, maskString, maskArguments } = require('data-guardian');

// Masking a string
// Output: "Se************123!"

console.log(maskString('connection to postgres://dbuser:SuperSecretPassword!@localhost:5432/mydb established'));
// output: "connection to po****es://db**er:Su**************************st:5432/mydb established"

// Masking an arbitary string with sensitive data
console.log(maskString('a dude once exposed his super secret A1vbcvc.De#3435?r password to the world but luckily we could help')); 
// Output: "a dude once exposed his super secret A1***********35?r password to the world but luckily we could help"

// Masking object's properties
const user = { username: 'johndoe', password: 'SuperSecretPassword!' };
// Output: { username: 'johndoe', password: 'Su***************d!' }

// Masking arguments list
console.log(maskArguments(['SensitiveArgument1', 'SensitiveArgument2'])); 
// Output: ["Se*****************1", "Se*****************2"]

📚 Defaults

By default, data-guardian masks the following data types in free-form strings and object properties:

  • credit card numbers
  • email addresses
  • IPv4 addresses
  • UUIDs
  • phone numbers
  • social security numbers
  • URLs
  • Passwords
  • Custom sensitive data (see Customization)

🛡️ Immutability

By default, data-guardian preserves the immutability of your data, meaning your original input remains untouched. However, if you prefer to alter the original data, you can do so by setting the immutability option to false.

const user = { password: 'SuperSecretPassword!' };
maskData(user, { immutable: false }); // This will mutate the `user` object
// Output: { password: 'Su***************d!' }

⚙️ Customization

With data-guardian, you're not limited to the predefined sensitive data types! You can extend its functionality by providing your own custom regular expressions for identifying and masking sensitive data in strings, or by providing a custom function to determine which keys to mask in objects:

// Define a custom regex that identifies a pattern "customSensitiveData: any-text-here"
const customRegExp = { customPattern: /customSensitiveData:\s*(\S+)/gi };

const data = {
    id: 1,
    name: 'Test Name',
    customField: 'customSensitiveData: verySensitive'
console.log(maskData(data, { customSensitiveContentRegExp: customRegExp })); 
// Output: { id: 1, name: 'Test Name', customField: 'cu******************************ve' }

// Custom regular expressions for string masking
const customPatterns = {
    secretCode: /my-secret-code-\d{3}/gi, // matches 'my-secret-code-123', 'my-secret-code-456', etc.

console.log(maskString('Here is my-secret-code-123!', { customPatterns }));
// Output: "Here is my-*********-123!"

const customMaskingLogic = (key) => {
// add your custom logic here. Return true for keys you want to mask
return ['customSensitiveKey', 'anotherSensitiveKey'].includes(key);

const data = { customSensitiveKey: 'HideThis', anotherSensitiveKey: 'AndThis', normalKey: 'ButNotThis' };
console.log(maskData(data, { keyCheck: customMaskingLogic })); 
// Output: { customSensitiveKey: 'Hi******s', anotherSensitiveKey: 'An******s', normalKey: 'ButNotThis' }

🌟 Advanced Usage

Masking Data in a Map, Set, and Error Instances

data-guardian extends its masking capabilities to Map, Set, and Error instances as well. Below are examples illustrating how to mask sensitive data stored in these structures:

Masking Data in a Map:

const sensitiveMap = new Map();
sensitiveMap.set('username', 'johndoe');
sensitiveMap.set('password', 'SuperSecretPassword!');

const maskedMap = maskData(sensitiveMap);
// Output: [["username", "johndoe"], ["password", "Su***************d!"]]

Masking Data in a Set:

const sensitiveSet = new Set(['SensitiveData1', 'SensitiveData2']);
const maskedSet = maskData(sensitiveSet);
// Output: ["Se**************1", "Se**************2"]

Masking Data in an Error:

const sensitiveError = new Error('Sensitive message containing user password: SuperSecretPassword!');
const maskedError = maskData(sensitiveError);
// Output: "Sensitive message containing user password: Su***************d!"

Remember, when working with Maps, the immutable option is especially handy as it prevents the original Map from being altered, ensuring data integrity and consistency across your application.

Custom Masking Configuration:

data-guardian allows for custom configuration through the IMaskDataOptions interface. You can specify a custom function to determine which keys to mask in objects, set a custom masking character, and define the length of characters to mask out among other options:

const customMaskingConfig = {
    keyCheck: (key) => key.includes('Sensitive'),
    maskingChar: '#',
    maskLength: 10,

const data = {
    id: 1,
    SensitiveInfo: 'VerySensitiveData',

console.log(maskData(data, customMaskingConfig));
// Output: { id: 1, SensitiveInfo: 'Very##########Data' }

Exclusion of certain matchers:

data-guardian allows for exclusion of certain matchers. This is useful when you want to mask all sensitive data except for a few. For example, you may want to mask all sensitive data except for the password in a URI.

const exampleString = 'I do not want to mask my credit card number 1234-5678-9012-3456 but my password SuperSecretPassword should not be visible';
console.log(maskString(exampleString, { excludeMatchers: ['creditCard'] }));
// Output: "I do not want to mask my credit card number 1234-5678-9012-3456 but my password Su***************rd should not be visible"

Explicit exclusion for masking:

data-guardian allows for explicit bypassing masking of potential sensitive content in strings by wrapping the content with '##'

const exampleString = 'SpanWidth01 is invalid!';
// Output: "Sp*******01 is invalid!"

const exampleNonMaskedString = '##SpanWidth01## is invalid!';
// Output: "SpanWidth01 is invalid!"

console.log(maskData({ username: 'johndoe', password: '##SuperSecretPassword!##' }));
// Output: { username: 'johndoe', password: 'SuperSecretPassword!' }

📜 API Reference

This section provides detailed information about the functions available in the Sensitive Content Masker library.



An alias for the keys of the sensitiveContentRegExp object.

declare const sensitiveContentRegExp: {
    readonly uuid: RegExp;
    readonly creditCard: RegExp;
    readonly ssn: RegExp;
    readonly url: RegExp;
    readonly ipv4: RegExp;
    readonly email: RegExp;
    readonly passwordSubstring: RegExp;
    readonly password: RegExp;
    readonly passwordInUri: RegExp;
    readonly passwordMention: RegExp;


A union type representing the characters that can be used for masking. Can be one of the following characters:

type MaskingChar = 'X' | 'x' | '$' | '/' | '.' | '*' | '#' | '+' | '@' | '-' | '_' | ' ';


An interface representing the available options for masking.

keyCheck (function): A function that checks if a key should have its value masked. Accepts a string and returns a boolean.
immutable (boolean): Whether the original data structure should be preserved, and an entirely new one created. Default is true.
customPatterns (object): An object where keys are custom types and values are RegExp objects used for identifying sensitive content.
maskingChar (MaskingChar): The character used for masking content.
maskLength (number): The length of the mask to apply on the sensitive content.
types (SensitiveContentKey[]): The types of sensitive content to check for.
customSensitiveContentRegExp (object): An object similar to customPatterns, but used only in certain masking contexts.
fixedMaskLength (boolean): When enabled, masks the sensitive content with a fixed number of characters. Default is 'false'.
excludeMatchers (SensitiveContentKey[]): The types of sensitive content to exclude from masking.

maskString(value: string, options?: Partial<IMaskOptions>): string

Masks sensitive parts of a string based on the provided options.


  • value (string): The string containing potential sensitive content that needs to be masked.
  • options (Partial, optional): A set of configurations for the masking process.

Return value

  • (string): The input string with sensitive content masked according to the specified options.

maskData<T>(data: T, options?: Partial<IMaskOptions>): T

Recursively masks sensitive data in an object, array, or any other nested structure based on the provided options. Will not mask objects with circular references.


  • data (T): The data structure containing potential sensitive information. It could be an object, array, Map, Set, etc.
  • options (Partial, optional): A set of configurations for the masking process, similar to the maskString function. Additionally, it uses the keyCheck function to decide if an object's key should have its value masked, based on the key name.

Return value

  • (T): A new data structure with the same type as the input, containing masked sensitive content. If immutable is false, it alters the original data; otherwise, it returns a new instance.

These functions are generic and designed to handle various types of data structures, ensuring sensitive information is adequately masked while retaining the original data format and type.

maskArguments(func: (...args: any[]) => any, options?: Partial<IMaskOptions>): (...args: any[]) => any

Wraps a function and masks sensitive information within the arguments passed to it, based on the provided options. This is particularly useful for logging or monitoring systems where function arguments may contain sensitive data.


  • func (Function): The original function that will be called with the masked arguments. This function takes any number of arguments and can return any type of data.
  • options (Partial, optional): A set of configurations for the masking process.

Return value

  • (Function): A new function that takes the same parameters as the original one. When this function is called, it masks the arguments as per the specified options and then calls the original function with these masked arguments. The return value of this new function is the same as that of the original function.

The maskArguments function is essential for scenarios where sensitive information might be passed to functions that log, transmit, or manipulate this data in ways that could lead to exposure. By masking arguments automatically, this method helps maintain data privacy and security without requiring significant changes to existing codebases.

⚠️ Disclaimer

data-guardian is designed to provide an additional layer of security by masking strings and object properties that contain sensitive information. However, it is not a substitute for comprehensive security practices. Ensure you follow industry standards and regulations for data protection and privacy.

🎈 Contributing

If you have ideas on how to improve data-guardian or want to report a bug, please open an issue or submit a pull request. We appreciate your help and contributions!

📜 License


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