How to check if an object is array-like but not array

Question

We can check whether a variable is array-like or array by Checking if an object is array-like.

How to check if a variable is array-like but not an array?

Update 1:

What I have tried so far is:

const car = { type: "Fiat", model: "500", color: "white" };
const cars = ["Saab", "Volvo", "BMW"];

function sum(a, b, c) {
    console.log(Array.prototype.isPrototypeOf(arguments));
    return a + b + c;
}

console.log(Array.prototype.isPrototypeOf(car));
console.log(Array.prototype.isPrototypeOf(cars));
result = sum(1, 2, 3)

I have use function sum because the documentation says:

arguments is an array-like object

So far it yields correct result. Please let me know whether I am on the right track.

I am assuming it has Array.prototype.forEach method then it is array-like. — Ahmad Ismail
– Ahmad Ismail, Commented May 25, 2023 at 17:03
@AhmadIsmail If an object supports .forEach() it doesn't mean it's array-like. — Scott Marcus
– Scott Marcus, Commented May 25, 2023 at 17:24

Tom · Accepted Answer · 2023-05-26 09:21:33Z

0

arguments in a function is an object with keys and values you do not need to check if it is array like.

function sum(a,b,c){
  console.log(typeof arguments, arguments);

}

const car = { type: "Fiat", model: "500", color: "white" };
const cars = ["Saab", "Volvo", "BMW"];

sum(1,2,3)
sum(car);
sum(cars);
sum(...cars);

If you want to sum every value passed to function sum just loop throuht arguments using for..in loop

function sum(){
  let total = 0;
  for(const key in arguments){
    total += arguments[key];
  }
  return total;
}

console.log(sum(1,2,3));

// strings as arguments
const cars = ["Saab", "Volvo", "BMW"];
console.log(...cars);

Make sure every arguments[key] is a number which can be summed otherwise strings will be concatenated

answered May 26, 2023 at 9:21

Tom

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3 Comments

Ahmad Ismail Over a year ago

I know i do not "check if it is array like". I used the argument just to have an array-like object. The question is not about how to use the arguments variable.

Tom Over a year ago

@AhmadIsmail In this case maybe this article can help link

Ahmad Ismail Over a year ago

Thank you very much. I am going through it right now.

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