Unexpected Behavior When Using Array.prototype.reduce with Sparse Arrays in JavaScript
I'm facing an unexpected behavior when using the `Array.prototype.reduce` method on a sparse array in JavaScript. I have a sparse array that looks like this: `const arr = [1, , 3, , 5];`. When I try to sum the elements using `reduce`, I get an unexpected result. Here’s the code snippet I’m using: ```javascript const arr = [1, , 3, , 5]; const sum = arr.reduce((acc, val) => acc + val, 0); console.log(sum); ``` Instead of getting `9`, which is what I expect from summing the defined elements, I'm actually getting `6`. I suspect this might be because of the empty slots in the sparse array. I tried using `filter` to remove the `undefined` values before applying `reduce`, like this: ```javascript const sumFiltered = arr.filter(val => val !== undefined).reduce((acc, val) => acc + val, 0); console.log(sumFiltered); ``` However, this approach feels less efficient, especially for larger arrays. I also explored using `map` to fill in default values for the `undefined` elements, but that doesn't seem to be optimal either. Am I misunderstanding how `reduce` works with sparse arrays, or is there a more efficient way to handle this situation? Additionally, what are the implications of using `reduce` on sparse arrays in performance terms? I'm using Node.js v14.17.0. Any insights would be greatly appreciated!