Using Array.isArray() 

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

Using instanceof Operator

The instanceof operator can be used to check if a variable is an instance of Array.

let arr = [1, 2, 3];
let notArray = "Hello";
console.log(arr instanceof Array);      // true
console.log(notArray instanceof Array); // false

Using constructor Property

You can check the constructor property of an object, but this method is not as reliable because the constructor property can be modified.

let arr = [1, 2, 3];
let notArray = "Hello";
console.log(arr.constructor === Array);      // true
console.log(notArray.constructor === Array); // false

While this works in most cases, it's generally not recommended due to potential issues with modifying the constructor property.

Recommended Method:

The best and most reliable way to check if a variable is an array in JavaScript is by using Array.isArray() because it is simple, clear, and works in all scenarios.