Guard JS

Validate input data and parameters with simple guard clauses.

🧪 Fully tested

😎 Includes TypeScript support

🤓 Read the post: Better data validation with Guard Clauses

import { guard } from "@phillcode/guard";

function someNumberMax10(someNumber) {
  guard(someNumber, "someNumber") // Name the parameter to generate a better error message
    .max(10); // Value must be a number <= 10
}

function someEmail(email) {
  guard(email, "email").email(); // Must be a valid email
}

function firstAndLastName(first, last) {
  guard(first, "firstName").minLength(3); // At least 3 characters long

  guard(last, "lastName")
    .optional() // The last name is optional
    .minLength(3); // If provided, it must also be at least 3 characters long
}

function performBuiltInTransformations(someString) {
  someString = guard(someString, "someString")
    .trim() // Ensure the value is a string and trim it
    .length(3, 15) // Must be 3-15 characters long
    .toLowerCase().value; // Lowercase the string and get the value
}

function guardElementsOfAnArray(arr) {
  arr = guard(arr, "arr")
    .useDefault([]) // If arr is null or undefined, default to an empty array
    .elements((g, index) => {
      g.max(10); // Every element must be a number <= 10
      console.log(index, g.value); // Log the index and value
    }).value;
}

function guardPropertiesOfAnObject(obj) {
  obj = guard(obj, "obj")
    .notEmpty() // Must have at least one property
    .entries((g, key) => {
      g.number(); // Every property must be a number
      console.log(key, g.value); // Log the key and value
    }).value; // Get the guarded value
}

function oneOfTwoParametersIsRequired(a, b) {
  guard(a, "a")
    .optional(b === null || b === undefined)
    .number(); // a is required if b is not provided
  guard(b, "b")
    .optional(a === null || a === undefined)
    .number(); // b is required if a is not provided
}

These are just some examples.

Have a look below at all the built-in guard and utility clauses to get a hold of everything you can do.

Included guard (validation) clauses

• array: Ensures that the value is a valid JavaScript array
• date: Ensures that the value is a valid JavaScript number
• equal: Ensures that the value exactly equals (===) the specified value
• email: Ensures that the value is a valid email address
• ensure: Runs the guarded value through the provided function, which is expected to return true in order for the guarded value to be considered valid. Use this to provide your own validation function
• hostname: Ensures that the value is a valid hostname (domain name)
• in: Ensures that the value matches one of the possible values
• instanceOf: Ensures that the guarded value is a valid instance of the specified class
• integer: Ensures that the value is in the valid integer
• isoDateTime: Ensures that the value is a valid ISO datetime string
• length: Ensures that the value is a string or array within the specified length (min and max)
• max: Ensures that the value is a number lesser than or equal to the specified value
• maxLength: Ensures that the value is a string or array with length lesser than or equal to the specified value
• min: Ensures that the value is a number greater than or equal to the specified value
• minLength: Ensures that the value is a string or array with length greater than or equal to the specified value
• notEqual: Ensures that the value, does NOT exactly equals (!==) the specified value
• notIn: Ensures that the value is not one of the specified values
• notEmpty: Ensures that the value is not empty. If the value is a string, it must have at least one character. If it is an array, it must have at least one element. If it is an object, it must have at least one property
• notEmptyOrWhitespace: Ensures that the value is a string with at least one character that is not a whitespace
• number: Ensures that the value is a valid JavaScript number
• object: Ensures that the value is a valid JavaScript object
• match: Ensures that the guarded value is a string and matches the provided regex pattern
• matchAny: Ensures that the guarded value is a string and matches at least one of the provided patterns
• range: Ensures that the value is a number in the specified range
• string: Ensures that the value is a valid JavaScript string
• unique: Ensures that the value is an array and that all of its entries are unique
• url: Ensures that the value is a valid URL
• hasValue: Returns a value indicating whether the guarded value is null or undefined

Included utility clauses

• coerceToBoolean: Coerces the guarded value into a Boolean value, guaranteed to be either true or false
• do: If the guarded value is not null nor undefined, runs it through the provided callback function
• elements: Steps into the items of the input value, when it is an array
• entries: Steps into the items of the input value, when it is an object
• makeUnique: If the value is present and is an Array, makes its elements unique
• matchAndFormat: Ensures that the guarded value is a string and matches the provided regex pattern. If matched, formats the value using the provided format string
• matchAnyAndFormat: Ensures that the guarded value is a string and matches at least one of the provided patterns. If matched, formats the value using the associated format string
• optional: Marks the guarded value as optional, so that guard functions will not throw an error if the value is null or undefined
• transform: Runs the guarded value through the provided transform function. Use this to provide your own transformation function
• toLowerCase: Makes a string lower case
• toUpperCase: Makes a string upper case
• trim: Trims the guarded string value
• useDefault: Provides a default value, in case the original is null or undefined

Install from NPM

npm install @phillcode/guard

yarn add @phillcode/guard