Introduction to kind-of

The kind-of library is a highly efficient utility for determining the kind or type of a JavaScript value. Perfect for developers who want to perform type checks and validation, kind-of saves time and enhances code readability. This guide covers the most useful APIs of kind-of with practical examples.

Key APIs of kind-of

Basic Type Checking

The primary function of kind-of is to determine the type of a value. Here’s how you can check basic data types:

const kindOf = require('kind-of');

console.log(kindOf(123));         // 'number'
console.log(kindOf('Hello'));     // 'string'
console.log(kindOf(true));        // 'boolean'
console.log(kindOf(null));        // 'null'
console.log(kindOf(undefined));   // 'undefined'

Complex Type Checking

kind-of also supports checking more complex data types:

console.log(kindOf([1, 2, 3]));       // 'array'
console.log(kindOf({ name: 'Joe' })); // 'object'
console.log(kindOf(() => {}));        // 'function'
console.log(kindOf(/abc/));           // 'regexp'
console.log(kindOf(new Date()));      // 'date'

Buffer and Promise Types

Check for Node.js-specific types such as Buffer and Promise:

console.log(kindOf(Buffer.from('data'))); // 'buffer'
console.log(kindOf(Promise.resolve()));   // 'promise'

kind-of in a Real-world Application

To showcase the usage of kind-of in a real-world scenario, here’s a small app that validates user inputs:

const kindOf = require('kind-of');

function validateUserInput(input) {
  if (kindOf(input) !== 'object' || kindOf(input.name) !== 'string' || kindOf(input.age) !== 'number') {
    throw new Error('Invalid user input');
  }
  return 'User input is valid.';
}

const userInput = {
  name: 'Alice',
  age: 30
};

try {
  console.log(validateUserInput(userInput)); // User input is valid.
} catch (error) {
  console.error(error.message);
}

const invalidUserInput = {
  name: 'Bob',
  age: 'thirty'
};

try {
  console.log(validateUserInput(invalidUserInput)); // Throws Error: Invalid user input
} catch (error) {
  console.error(error.message);
}

kind-of proves to be an extremely helpful library in ensuring that data conforms to expected types, ultimately aiding in debugging and validation processes.

Start using kind-of to make your JavaScript code more reliable and easier to maintain.

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