How to check if an object is an array or not? Provide some code.

The best way to find whether an object is instance of a particular class or not using toString method from Object.prototype

var arrayList = [1 , 2, 3];

One of the best use cases of type checking of an object is when we do method overloading in JavaScript. For understanding this let say we have a method called greet which take one single string and also a list of string, so making our greet method workable in both situation we need to know what kind of parameter is being passed, is it single value or list of value?

function greet(param) {
  if() {
    // here have to check whether param is array or not
  }
  else {
  }
}

However, in above implementation it might not necessary to check type for array, we can check for single value string and put array logic code in else block, let see below code for the same.

 function greet(param) {
   if(typeof param === 'string') {
   }
   else {
     // If param is of type array then this block of code would execute
   }
 }

Now it’s fine we can go with above two implementations, but when we have a situation like a parameter can be single value, array, and object type then we will be in trouble.

Coming back to checking type of object, As we mentioned that we can use Object.prototype.toString

if(Object.prototype.toString.call(arrayList) === '[object Array]') {
  console.log('Array!');
}

If you are using jQuery then you can also used jQuery isArray method:

if($.isArray(arrayList)) {
  console.log('Array');
} else {
  console.log('Not an array');
}

FYI jQuery uses Object.prototype.toString.call internally to check whether an object is an array or not.

In modern browser, you can also use:

Array.isArray(arrayList);

Array.isArray is supported by Chrome 5, Firefox 4.0, IE 9, Opera 10.5 and Safari 5