Implement a Generic Filter Function

Problem Implement your own generic, reusable filter function in JavaScript, mirroring Array.prototype.filter: it takes a predicate callback and returns a new array containing the elements for which the predicate returns truthy.

Requirements

• myFilter(array, predicate, thisArg?) -> Array (or Array.prototype.myFilter = function(predicate, thisArg) {...}).
• Predicate invoked as predicate(element, index, array) — all three arguments.
• Returns a new array; the input is never mutated.
• Truthy (not strictly true) return values include the element.
• Skips holes in sparse arrays.

Areas to design

• The iteration contract (all three predicate arguments, thisArg, truthiness).
• Correct sparse-array / holes handling and length snapshotting.
• Prototype extension vs standalone function, and edge/error cases.