Type Guards TS

type-guards-ts is a TypeScript library providing a collection of type guard functions to help you perform runtime type checking and type narrowing. This library includes functions to check if a value is of a certain type (e.g., isBoolean) as well as functions to check if a value is not of a certain type (e.g., isNotBoolean).

Index

• Installation
• How to Use
• Available Type Guards
• How to Use Each Type Guard
  • isBigInt
  • isBoolean
  • isFunction
  • isNull
  • isNumber
  • isObject
  • isString
  • isSymbol
  • isUndefined
  • isArray
  • isDate
  • isNotBigInt
  • isNotBoolean
  • isNotFunction
  • isNotNull
  • isNotNumber
  • isNotObject
  • isNotString
  • isNotSymbol
  • isNotUndefined
  • isNotArray
  • isNotDate
• Future Releases

Installation

To install the package, run the following command:

npm install type-guards-ts

How to Use

To use the type guards provided by type-guards-ts, you can import the required functions from the package and use them in your TypeScript code. Here’s a quick example:

import { isBoolean } from "type-guards-ts";

const value: unknown = true;

if (isBoolean(value)) {
  // TypeScript now knows that `value` is a boolean
  console.log("The value is a boolean.");
} else {
  console.log("The value is not a boolean.");
}

Available Type Guards

• isBigInt
• isBoolean
• isFunction
• isNull
• isNumber
• isObject
• isString
• isSymbol
• isUndefined
• isArray
• isDate
• isNotBigInt
• isNotBoolean
• isNotFunction
• isNotNull
• isNotNumber
• isNotObject
• isNotString
• isNotSymbol
• isNotUndefined
• isNotArray
• isNotDate

How to Use Each Type Guard

isBigInt

Checks if a value is a BigInt.

import { isBigInt } from "type-guards-ts";

const value: unknown = BigInt(123);

if (isBigInt(value)) {
  console.log("The value is a BigInt.");
} else {
  console.log("The value is not a BigInt.");
}

isBoolean

Checks if a value is a boolean.

import { isBoolean } from "type-guards-ts";

const value: unknown = true;

if (isBoolean(value)) {
  console.log("The value is a boolean.");
} else {
  console.log("The value is not a boolean.");
}

isFunction

Checks if a value is a function.

import { isFunction } from "type-guards-ts";

const value: unknown = () => {};

if (isFunction(value)) {
  console.log("The value is a function.");
} else {
  console.log("The value is not a function.");
}

isNull

Checks if a value is null.

import { isNull } from "type-guards-ts";

const value: unknown = null;

if (isNull(value)) {
  console.log("The value is null.");
} else {
  console.log("The value is not null.");
}

isNumber

Checks if a value is a number.

import { isNumber } from "type-guards-ts";

const value: unknown = 42;

if (isNumber(value)) {
  console.log("The value is a number.");
} else {
  console.log("The value is not a number.");
}

isObject

Checks if a value is an object.

import { isObject } from "type-guards-ts";

const value: unknown = { key: "value" };

if (isObject(value)) {
  console.log("The value is an object.");
} else {
  console.log("The value is not an object.");
}

isString

Checks if a value is a string.

import { isString } from "type-guards-ts";

const value: unknown = "Hello, world!";

if (isString(value)) {
  console.log("The value is a string.");
} else {
  console.log("The value is not a string.");
}

isSymbol

Checks if a value is a symbol.

import { isSymbol } from "type-guards-ts";

const value: unknown = Symbol("symbol");

if (isSymbol(value)) {
  console.log("The value is a symbol.");
} else {
  console.log("The value is not a symbol.");
}

isUndefined

Checks if a value is undefined.

import { isUndefined } from "type-guards-ts";

const value: unknown = undefined;

if (isUndefined(value)) {
  console.log("The value is undefined.");
} else {
  console.log("The value is not undefined.");
}

isArray

Checks if a value is an array.

import { isArray } from "type-guards-ts";

const value: unknown = [];

if (isArray(value)) {
  console.log("The value is an array.");
} else {
  console.log("The value is not array.");
}

Below is an example of documentation in Markdown format that teaches how to use the isDate and isNotDate type guards.

isDate

Description:
Checks whether the provided value is a Date object.
This function verifies if the given value is a Date by first checking whether it is an instance of Date. It also uses Object.prototype.toString to handle cases where the Date object might come from a different execution context.

Usage Example:

import { isDate } from "type-guards-ts";

const value: unknown = new Date();

if (isDate(value)) {
  console.log("The value is a Date:", value);
} else {
  console.log("The value is not a Date.");
}

isNotBigInt

Checks if a value is not a BigInt.

import { isNotBigInt } from "type-guards-ts";

const value: unknown = 123;

if (isNotBigInt(value)) {
  console.log("The value is not a BigInt.");
} else {
  console.log("The value is unknown.");
}

isNotBoolean

Checks if a value is not a boolean.

import { isNotBoolean } from "type-guards-ts";

const value: unknown = "true";

if (isNotBoolean(value)) {
  console.log("The value is not a boolean.");
} else {
  console.log("The value is unknown.");
}

isNotFunction

Checks if a value is not a function.

import { isNotFunction } from "type-guards-ts";

const value: unknown = "function";

if (isNotFunction(value)) {
  console.log("The value is not a function.");
} else {
  console.log("The value is unknown.");
}

isNotNull

Checks if a value is not null.

import { isNotNull } from "type-guards-ts";

const value: unknown = "not null";

if (isNotNull(value)) {
  console.log("The value is not null.");
} else {
  console.log("The value is unknown.");
}

isNotNumber

Checks if a value is not a number.

import { isNotNumber } from "type-guards-ts";

const value: unknown = "42";

if (isNotNumber(value)) {
  console.log("The value is not a number.");
} else {
  console.log("The value is unknown.");
}

isNotObject

Checks if a value is not an object.

import { isNotObject } from "type-guards-ts";

const value: unknown = "object";

if (isNotObject(value)) {
  console.log("The value is not an object.");
} else {
  console.log("The value is unknown.");
}

isNotString

Checks if a value is not a string.

import { isNotString } from "type-guards-ts";

const value: unknown = 123;

if (isNotString(value)) {
  console.log("The value is not a string.");
} else {
  console.log("The value is unknown.");
}

isNotSymbol

Checks if a value is not a symbol.

import { isNotSymbol } from "type-guards-ts";

const value: unknown = "symbol";

if (isNotSymbol(value)) {
  console.log("The value is not a symbol.");
} else {
  console.log("The value is unknown.");
}

isNotUndefined

Checks if a value is not undefined.

import { isNotUndefined } from "type-guards-ts";

const value: unknown = "defined";

if (isNotUndefined(value)) {
  console.log("The value is not undefined.");
} else {
  console.log("The value is unknown.");
}

isNotArray

Checks if a value is not an array.

import { isNotArray } from "type-guards-ts";

const value: unknown = "not array";

if (isNotArray(value)) {
  console.log("The value is not an array.");
} else {
  console.log("The value is not unknown.");
}

isNotDate

Description:
Determines if the provided value is not a Date object.
This type guard leverages the isDate helper function to check if a value is not a Date. If the value is not a Date, the function returns true and narrows the type accordingly.

Usage Example:

import { isNotDate } from "type-guards-ts";

const value: unknown = "2023-08-24"; // Example value that is not a Date

if (isNotDate(value)) {
  console.log("The value is not a Date:", value);
} else {
  console.log("The value is a Date.");
}

Future Releases

Currently, this package focuses on type guards for primitive types. However, we're actively working on expanding the library to include type guards for non-primitive types. Stay tuned for future releases where you'll find new and enhanced functionalities!

Keep your code safe and type-safe with type-guards-ts! 🚀