The Array.of() static method creates a new Array
instance from a variable number of arguments, regardless of number or type of the
arguments.
Syntax
Array.of()
Array.of(element1)
Array.of(element1, element2)
Array.of(element1, element2, /* …, */ elementN)
Parameters
element1, …,elementN- : Elements used to create the array.
Return value
A new Array instance.
Description
The difference between Array.of() and the Array() constructor is in the handling of single arguments: Array.of(7) creates an array with a single element, 7, whereas Array(7) creates an empty array with a length property of 7. (That implies an array of 7 empty slots, not slots with actual undefined values.)
Array.of(7); // [7]
Array(7); // array of 7 empty slots
Array.of(1, 2, 3); // [1, 2, 3]
Array(1, 2, 3); // [1, 2, 3]
The Array.of() method is a generic factory method. For example, if a subclass of Array inherits the of() method, the inherited of() method will return new instances of the subclass instead of Array instances. In fact, the this value can be any constructor function that accepts a single argument representing the length of the new array, and the constructor will be called with the number of arguments passed to of(). The final length will be set again when all elements are assigned. If the this value is not a constructor function, the plain Array constructor is used instead.
Examples
Using Array.of()
Array.of(1); // [1]
Array.of(1, 2, 3); // [1, 2, 3]
Array.of(undefined); // [undefined]
Calling of() on non-array constructors
The of() method can be called on any constructor function that accepts a single argument representing the length of the new array.
function NotArray(len) {
console.log("NotArray called with length", len);
}
console.log(Array.of.call(NotArray, 1, 2, 3));
// NotArray called with length 3
// NotArray { '0': 1, '1': 2, '2': 3, length: 3 }
console.log(Array.of.call(Object)); // [Number: 0] { length: 0 }
When the this value is not a constructor, a plain Array object is returned.
console.log(Array.of.call({}, 1)); // [ 1 ]