JS: arguments (object)

What is the argument object

• The arguments is a builtin variable, available in function body of functions defined via the keyword function. It is not available in Arrow Function.
• The arguments object is a Array-Like Object. Each index is the value of arguments of a function call.

function ff() {
 return arguments;
}

// show the arguments object
console.log(ff(800, 638));
// [Arguments] { "0": 800, "1": 638 }

// show its length
console.log(ff(800, 638).length);
// 2

// show all its keys
console.log(Reflect.ownKeys(ff(800, 638)));
// [ "0", "1", "length", "callee", Symbol(Symbol.iterator) ]

// not a true array
console.log(Array.isArray(ff()) === false);
// true

Purpose of the argument object

In 1995, the purpose of the argument object was to allow function to take arbitrary number of arguments, such as plus function.

It is no longer needed today because Rest Parameters feature was added to JavaScript.

• JS: Function Rest Parameters

🟢 TIP: never use the argument object