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Check types in JavaScript

Check types in JavaScript

Write a JavaScript function to check the types for each

  • isArray – returns true for an array, else false
  • isFunction – returns true for functions, else false
  • isObject – returns true for objects, else false
  • isPlainObject – returns true for plain objects; otherwise, it is false (arrays, functions, dates, etc.).

🔗 Type Utilities 🟢 Easy🧩 Pattern – JavaScript Essentials

Note ✍️

const obj = {}; // or: const obj = new Object();Code language: JavaScript (javascript)

This object inherits from Object.prototype, so it has access to built-in methods like .toString(), .hasOwnProperty().

const obj = Object.create(null);Code language: JavaScript (javascript)

This means it doesn’t inherit any properties or methods (like .toString, .hasOwnProperty, etc.) but it is an object.

JS Code to check all types

export function isArray(value) {
  return Array.isArray(value);
}

export function isFunction(value) {
  return typeof value === "function";
}

export function isObject(value) {
  if (value === null) {
    return false;
  }
  return typeof value === "object" || typeof value === "function";
}

export function isPlainObject(value) {
  if (typeof value !== "object" || value === null) return false;
  const proto = Object.getPrototypeOf(value);
  return proto === Object.prototype || proto === null;
}Code language: JavaScript (javascript)
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