array-extend.js

'use strict';

class ExtendedArray extends Float64Array {
	double () {}
}

while (true) {
	let thing = new ExtendedArray(1);

	console.log('The method "double" is', typeof thing.double);
	console.log('Is it still an ExtendedArray?', thing instanceof ExtendedArray);
	console.log('Is it still an Float64Array?', thing instanceof Float64Array);

	if (thing.double === undefined) {
		throw new Error('Method "double" should not be undefined');
	}
}