Type operators in JavaScript are used to determine or interact with the type of a value or variable. They help you check types, identify instances of classes or objects, and more. Here’s a detailed look at the main type operators:

1. typeof Operator

• Purpose: Returns a string indicating the type of a variable or expression.
• Syntax: typeof operand
• Example:

  let num = 42;
  console.log(typeof num); // 'number'
  
  let str = 'Hello';
  console.log(typeof str); // 'string'
  
  let obj = {};
  console.log(typeof obj); // 'object'
  
  let arr = [1, 2, 3];
  console.log(typeof arr); // 'object' (arrays are objects in JavaScript)
  
  let func = function() {};
  console.log(typeof func); // 'function'
  
  let und;
  console.log(typeof und); // 'undefined'
  

2. instanceof Operator

• Purpose: Tests whether an object is an instance of a specific constructor or class.

• Syntax: object instanceof constructor

• Example:

  let arr = [1, 2, 3];
  console.log(arr instanceof Array); // true
  
  let date = new Date();
  console.log(date instanceof Date); // true
  
  let obj = {};
  console.log(obj instanceof Object); // true
  

  • Note: instanceof checks the prototype chain, so it can determine if an object was created from a specific constructor or class.

3. Array.isArray() Method

• Purpose: Determines whether a value is an array. This is a built-in method rather than an operator, but it's commonly used for type checking.
• Syntax: Array.isArray(value)
• Example:

  let arr = [1, 2, 3];
  console.log(Array.isArray(arr)); // true
  
  let str = 'Hello';
  console.log(Array.isArray(str)); // false
  

4. typeof with Null Values

• Note: typeof returns "object" for null, which is considered a historical bug in JavaScript.
• Example:

  let n = null;
  console.log(typeof n); // 'object'
  

Key Points:

• Primitive Types: typeof can distinguish between primitive types like number, string, boolean, undefined, and symbol.
• Objects and Functions: typeof returns "object" for objects and arrays (since arrays are a type of object) and "function" for functions.
• Instance Checking: instanceof is useful for checking if an object was created by a specific constructor or class, and is handy for custom types and inheritance hierarchies.