Question

我是编程领域的新手，所以我会在我的javascript问题中给予我（如果是）简单的答案。

   at System.Data.Entity.Internal.ThrowingMonitor.EnsureNotEntered()
   at System.Data.Entity.Core.Objects.ObjectQuery`1.System.Data.Entity.Infrastructure.IDbAsyncEnumerable<T>.GetAsyncEnumerator()
   at System.Data.Entity.Internal.Linq.InternalQuery`1.GetAsyncEnumerator()
   at System.Data.Entity.Infrastructure.DbQuery`1.System.Data.Entity.Infrastructure.IDbAsyncEnumerable<TResult>.GetAsyncEnumerator()
   at System.Data.Entity.Infrastructure.IDbAsyncEnumerableExtensions.ForEachAsync[T](IDbAsyncEnumerable`1 source, Action`1 action, CancellationToken cancellationToken)
   at System.Data.Entity.Infrastructure.IDbAsyncEnumerableExtensions.ToListAsync[T](IDbAsyncEnumerable`1 source, CancellationToken cancellationToken)
   at System.Data.Entity.Infrastructure.IDbAsyncEnumerableExtensions.ToListAsync[T](IDbAsyncEnumerable`1 source)
   at System.Data.Entity.QueryableExtensions.ToListAsync[TSource](IQueryable`1 source)
   at xyz.desk.app.ccm.business.Service.CostsService.<GetCosts>d__7.MoveNext() in D:\Dev\ThatCrazyPluginProject\desk\app\xyz.desk.app.ccm.business\Service\CostsService.cs:line 89
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at xyz.desk.app.ccm.plugin.costplan.constructionprogress.ViewModel.ContructionProgressCostPlanViewModel.<LoadData>d__58.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
   at xyz.desk.app.ccm.plugin.settlementscheduleshost.ViewModel.SettlementSchedulesHostViewModel.<LoadCurrentSection>d__67.MoveNext() in D:\Dev\ThatCrazyPluginProject\desk\app\xyz.desk.app.ccm.ui\ViewModel\SettlementSchedulesHostViewModel.cs:line 307
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
   at xyz.desk.app.ccm.plugin.settlementscheduleshost.ViewModel.SettlementSchedulesHostViewModel.<LoadData>d__65.MoveNext() in D:\Dev\ThatCrazyPluginProject\desk\app\xyz.desk.app.ccm.ui\ViewModel\SettlementSchedulesHostViewModel.cs:line 282
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
   at xyz.desk.app.ccm.ui.ViewModel.ProjectViewModel.<LoadCurrentSection>d__115.MoveNext() in D:\Dev\ThatCrazyPluginProject\desk\app\xyz.desk.app.ccm.ui\ViewModel\ProjectViewModel.cs:line 763
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
   at xyz.desk.app.ccm.ui.ViewModel.ProjectViewModel.<<get_PluginsCv>b__21_0>d.MoveNext() in D:\Dev\ThatCrazyPluginProject\desk\app\xyz.desk.app.ccm.ui\ViewModel\ProjectViewModel.cs:line 120

有人可以一步一步地解释这些场景背后会发生什么？因为我无法理解为什么el会分配给我...

提前谢谢

Answer 1

这是非常基本的，只是尝试使用console.log来查看传递的实际值我已经提供了一些注释来帮助。

var years = [1990, 1965, 1937, 2005, 1998];

function arrayCalc(arr, fn) {//fn is function which will execute with current array element as argument
var arrRes = [];
for (var i = 0; i < arr.length; i++) {
    arrRes.push(fn(arr[i])); //fn:calculateAge(arr[i])
}
return arrRes;
}

function calculateAge(el) {//el is argument 
return 2018 - el;//substract the argument from 2018
}
var ages = arrayCalc(years, calculateAge);//passing calculateAge function as argument as function pointer
console.log(ages);

Answer 2

for循环中的i用于引用数组中的索引：arr[0] = 1990, arr[1] = 1965, arr[2] = 1937 etc.

在这种情况下，for循环

for (var i = 0; i < arr.length; i++) {
    arrRes.push(fn(arr[i]));
}

在数组中的每个元素上调用传递的函数fn（对于calculateAge（）：var ages = arrayCalc(years, calculateAge);）。该函数在将元素作为参数传入后使用el来引用该元素。

Answer 3

设置数组非常基本

//setting a array
var years = [1990, 1965, 1937, 2005, 1998]; 

//creating a function
function calculateAge(el) {
   return 2018 - el; // this will subtract every el with 2018
}

//calling a function, pass year variable & calculateAge function as argument of arrayCalc function and store its result on ages variable
var ages = arrayCalc(years, calculateAge);
console.log(ages); // show the result on console

如果我告诉你arrayCalc(arr, fn)，这就是幕后发生的事情 for循环处理years数组的每个元素并调用calculateAge()方法，在通过 2018 减去它后得到结果，并将结果推送到{每次{1}}数组，最后返回arrRes并将其分配给arrRes变量。

ages

输出： var arrRes = [] var result1 = 2018-1990; arrRes = [result1]; var result2 = 2018-1965; arrRes = [result1,result2]; var result3 = 2018-1937; arrRes = [result1,result2,result3]; var result4 = 2018-2005; arrRes = [result1,result2,result3,result4]; var result5 = 2018-1998; arrRes = [result1,result2,result3,result4,result5];

javascript传递函数作为参数

3 个答案: