[英]Uncaught TypeError: undefined is not a function when using highcharts
[英]Uncaught TypeError: element is undefined when using generator function
我有以下 javascript 片段:
/**
* 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])
當我在瀏覽器控制台中運行它時,我得到Uncaught TypeError: element is undefined
錯誤,我似乎無法發現我的代碼中的錯誤在哪里。
您不能使用iterable[0]
訪問生成器中的第一個元素。 您需要獲取迭代器並對其進行迭代:
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;
}
或者,只需使用undefined
初始化maximalElement
,如果 iterable 為空,則無論如何都可能發生這種情況:
function maxBy(iterable, fn) {
let maximalElement;
for (let element of iterable) {
if (maximalElement === undefined || fn(element) > fn(maximalElement)) {
maximalElement = element;
}
}
return maximalElement;
}
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