Fill
Problem statement
Implement a function fill(array, value, [start=0], [end=array.length]) that fills an array with values from start up to, but not including, end.
Note: This method mutates the original array.
Example
fill([1, 2, 3], 'a'); // ['a', 'a', 'a']
fill([4, 6, 8, 10], '*', 1, 3); // [4, '*', '*', 10]How to approach Fill
The strategy an interviewer expects you to reach for.
fill mutates a range in-place — the interview is mostly about index normalization, not the loop. Naive move Loop from start to end without handling negatives or clamping. Where it breaks Negative start/end count from the end. Out-of-range values clamp. end defaults to length. You must mutate the same array reference and return it. The fix Normalize start/end exactly like the spec (negative → length+index, clamp). Then assign array[i] = value for i in [start, end). Remember: Normalize indexes first; the write loop is the easy part. Say this in the interview: I'd normalize start and end the way Array.prototype.fill does — including negatives — then mutate that slice in place and return the same array.
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