Javascript 为什么不是'；这不是reduceworking（JS）的递归定义吗？

我试图使用递归函数重新定义Javascript的reduce。 这是我的尝试，但没有成功。如果有人能稍微改变一下，让它工作起来，那就太好了，因为我会更好地理解它。（这是一个练习）

它给了我以下神秘的错误信息，我不知道如何解释：

/usr/local/lib/node_modules/functional-javascript-workshop/exercises/basic_recursion/exercise.js:13
    prev[curr] = ++prev[curr] || 1
                            ^

TypeError: Cannot create property 'undefined' on string 'exercitation'
    at /usr/local/lib/node_modules/functional-javascript-workshop/exercises/basic_recursion/exercise.js:13:29
    at reduce (/home/david/node-school/functional-workshop/solution.js:7:28)
    at /usr/local/lib/node_modules/functional-javascript-workshop/exercises/basic_recursion/exercise.js:12:10
    at obtainResult (/usr/local/lib/node_modules/functional-javascript-workshop/exercises/runner.js:100:21)
    at Exercise.<anonymous> (/usr/local/lib/node_modules/functional-javascript-workshop/exercises/runner.js:66:27)
    at next (/usr/local/lib/node_modules/functional-javascript-workshop/node_modules/workshopper-exercise/exercise.js:188:19)
    at /usr/local/lib/node_modules/functional-javascript-workshop/node_modules/workshopper-exercise/exercise.js:195:7
    at Exercise.<anonymous> (/usr/local/lib/node_modules/functional-javascript-workshop/exercises/runner.js:34:5)
    at next (/usr/local/lib/node_modules/functional-javascript-workshop/node_modules/workshopper-exercise/exercise.js:188:19)
    at /usr/local/lib/node_modules/functional-javascript-workshop/node_modules/workshopper-exercise/exercise.js:195:7

/usr/local/lib/node_modules/functional javascript workshop/exercises/basic_recursion/exercise.js:13
上一次[当前]=++上一次[当前]| 1
^
TypeError:无法在字符串“exercuition”上创建属性“undefined”
at/usr/local/lib/node_modules/functional javascript workshop/exercises/basic_recursion/exercise.js:13:29
在reduce（/home/david/node school/functional workshop/solution.js:7:28）
at/usr/local/lib/node_modules/functional javascript workshop/exercises/basic_recursion/exercise.js:12:10
在获得结果时（/usr/local/lib/node_modules/functional javascript workshop/exercises/runner.js:100:21）
在运动中。（/usr/local/lib/node_modules/functional javascript workshop/exercises/runner.js:66:27）
接下来（/usr/local/lib/node_modules/functional javascript workshop/node_modules/workshopper exercise/exercise.js:188:19）
at/usr/local/lib/node_modules/functional javascript workshop/node_modules/workshopper exercise/exercise.js:195:7
在运动中。（/usr/local/lib/node_modules/functional javascript workshop/exercises/runner.js:34:5）
接下来（/usr/local/lib/node_modules/functional javascript workshop/node_modules/workshopper exercise/exercise.js:188:19）
at/usr/local/lib/node_modules/functional javascript workshop/node_modules/workshopper exercise/exercise.js:195:7

您需要更新累加器：

功能减少（arr、fn、acc）{
if（阵列长度）{
var newArr=arr.slice（1，arr.length）；
acc=fn（arr[0]，acc）
收益减少（新收益、fn、acc）；
}否则{
返回acc；
}
}
log（reduce（[1,2,3]，（val，sum）=>sum+val，0））

您忘记将累加器的当前值，即

initial

，传递到

fn

调用中。

正如其他人所指出的，您没有将累加器传递到

fn

。如果您很好奇，

reduce

可以用一个三元（

？：

）表达式来表示–而且，

arr.slice（1）

将从

1

切片到数组的末尾；在这种情况下，不需要指定切片的结尾

const reduce=（arr、fn、acc）=>
arr.length==0
? 行政协调会
：减少（arr.slice（1），fn，fn（acc，arr[0]））
常数加=（x，y）=>x+y
log（reduce（[1,2,3]，add，0））/6

只是想知道：

if（arr.length）

有效吗？我总是使用

if（arr.length>0）

…您没有向我们显示正确的代码。在您的

解决方案.js

的第7行调用后，

exercise.js

中出现错误。@Danmoreng，它测试真实值

fn

？

initial

应该是数组中元素的

索引吗？@guest271314 fn是用于减少数组的任何函数dude遵守
/usr/local/lib/node_modules/functional-javascript-workshop/exercises/basic_recursion/exercise.js:13
    prev[curr] = ++prev[curr] || 1
                            ^

TypeError: Cannot create property 'undefined' on string 'exercitation'
    at /usr/local/lib/node_modules/functional-javascript-workshop/exercises/basic_recursion/exercise.js:13:29
    at reduce (/home/david/node-school/functional-workshop/solution.js:7:28)
    at /usr/local/lib/node_modules/functional-javascript-workshop/exercises/basic_recursion/exercise.js:12:10
    at obtainResult (/usr/local/lib/node_modules/functional-javascript-workshop/exercises/runner.js:100:21)
    at Exercise.<anonymous> (/usr/local/lib/node_modules/functional-javascript-workshop/exercises/runner.js:66:27)
    at next (/usr/local/lib/node_modules/functional-javascript-workshop/node_modules/workshopper-exercise/exercise.js:188:19)
    at /usr/local/lib/node_modules/functional-javascript-workshop/node_modules/workshopper-exercise/exercise.js:195:7
    at Exercise.<anonymous> (/usr/local/lib/node_modules/functional-javascript-workshop/exercises/runner.js:34:5)
    at next (/usr/local/lib/node_modules/functional-javascript-workshop/node_modules/workshopper-exercise/exercise.js:188:19)
    at /usr/local/lib/node_modules/functional-javascript-workshop/node_modules/workshopper-exercise/exercise.js:195:7