I have the following javascript snippet:
/**
* Returns the maximal element in the `iterable` as calculated by the given function
* @param {Iterable} iterable - iterable to find the maximal element in
* @param {function} fn - function to calculate the maximal element
*
* @returns {any} - maximal element in the `iterable`
*/
function maxBy(iterable, fn) {
let maximalElement = iterable[0];
for (let element of iterable) {
if (fn(element) > fn(maximalElement)) {
maximalElement = element;
}
}
return maximalElement;
}
// example generator function
generator = function* () {
yield [3,4]
yield [4,6]
}
maxBy(generator(), element => element[1])
When I run this in browser console, I get Uncaught TypeError: element is undefined error and I can't seem to spot where's the error in my code.
You cannot use iterable[0] to access the first element in a generator. You'll need to get the iterator and iterate it:
function maxBy(iterable, fn) {
const iterator = iterable[Symbol.iterator]();
const first = iterator.next();
if (first.done) return;
let maximalElement = first.value;
for (let element of iterator) {
if (fn(element) > fn(maximalElement)) {
maximalElement = element;
}
}
return maximalElement;
}
Alternatively, just initialise maximalElement with undefined, this might happen anyway if the iterable is empty:
function maxBy(iterable, fn) {
let maximalElement;
for (let element of iterable) {
if (maximalElement === undefined || fn(element) > fn(maximalElement)) {
maximalElement = element;
}
}
return maximalElement;
}