The distinction between array literals and array constructors may seem subtle, but it can have significant implications for your code. While the difference is often discussed, there appears to be another nuance that has not been highlighted in previous explanations. Consider the following scenarios:
var x = new Array(5); // [undefined x 5];
var newArr = x.map(function () {return 'newValue'});
console.log(newArr); // [undefined x 5];
vs
var y = [undefined, undefined, undefined, undefined, undefined];
var newArr = y.map(function () {return 'newValue'});
console.log(newArr); // ['newValue', 'newValue', 'newValue', 'newValue', 'newValue'];
One might assume that both x and y are instances of an array and would yield the same results when using the .map method. However, the actual outcome reveals a discrepancy; x returns an unmappable array while y produces the expected mapping.
What causes this disparity in behavior between x and y regarding the .map method?
Your insights on this matter would be greatly appreciated.