[英]splice expected to remove multiple elements, but only removes one
I'm using splice to remove the last n
number of elements on an array (denoted by quizResponseCountToRemove
).我正在使用 splice 删除数组上的最后
n
个元素(由quizResponseCountToRemove
表示)。
However, in its currently implementation, it only removes 1 element.但是,在其当前的实现中,它只删除了 1 个元素。
Is there any particular reason for this?这有什么特别的原因吗?
My code is as follows;我的代码如下;
static removeCourseContentElementQuizResponseCount(
course: ICourse,
courseContents: ICourseContent[],
selectedCourseContentUid: string,
selectedCourseModule: number,
quizResponseCountToRemove: number
): ICourse {
courseContents.map((courseContent) => {
if (courseContent.uid === selectedCourseContentUid) {
courseContent.quiz.options.splice(-1, quizResponseCountToRemove);
if (courseContent.quiz.answer > courseContent.quiz.options.length) {
courseContent.quiz.answer = 1;
}
}
});
course.modules[selectedCourseModule].content = courseContents;
return course;
}
Update更新
It seems I have misunderstood how splice works.看来我误解了 splice 的工作原理。 I want splice to work backwards from the last element.
我希望 splice 从最后一个元素向后工作。 So in an array
['test1', 'test2', 'test3', 'test4']
, if quizResponseCountToRemove
is 2 then I end up with ['test1', 'test2']
.因此,在数组
['test1', 'test2', 'test3', 'test4']
中,如果quizResponseCountToRemove
为 2,那么我最终得到['test1', 'test2']
。
If you pass splice
a negative number for the first argument, that's an offset from the end of the array at which to perform the splice action.如果您为第一个参数传递一个负数
splice
,则这是从执行拼接操作的数组末尾的偏移量。 You're passing -1
, so it'll perform its action on the last entry in the array.您正在传递
-1
,因此它将对数组中的最后一个条目执行其操作。 By definition, there's only one last entry in the array, so it doesn't matter how large quizResponseCountToRemove
is.根据定义,数组中只有最后一个条目,因此
quizResponseCountToRemove
有多大并不重要。 If it's any number over 0
, only one element (the last one) will be removed.如果它是任何超过
0
的数字,则只会删除一个元素(最后一个)。
In a comment you've said:在评论中你说:
I want splice to work backwards from the last element.
我希望 splice 从最后一个元素向后工作。 So in an array
['test1', 'test2', 'test3', 'test4']
, ifquizResponseCountToRemove
is2
then I end up with['test1', 'test2']
所以在一个数组
['test1', 'test2', 'test3', 'test4']
中,如果quizResponseCountToRemove
是2
那么我最终得到['test1', 'test2']
In that case, you want to start quizResponseCountToRemove
from the end, so you could pass in -quizResponseCountToRemove
:在这种情况下,您想从最后开始
quizResponseCountToRemove
,因此您可以传入-quizResponseCountToRemove
:
courseContent.quiz.options.splice(-quizResponseCountToRemove, quizResponseCountToRemove);
...but that's unnecessarily complicated. ......但这太复杂了。 To truncate an array, you can just assign to its
length
:要截断数组,您可以分配给它的
length
:
courseContent.quiz.options.length -= quizResponseCountToRemove;
If it's possible that quizResponseCountToRemove
might be larger than the array's length, you'll need to ensure you don't try to assign a negative number to length
(which will cause an error):如果
quizResponseCountToRemove
可能大于数组的长度,您需要确保不要尝试为length
分配负数(这会导致错误):
courseContent.quiz.options.length = Math.max(0, courseContent.quiz.options.length - quizResponseCountToRemove);
Live Example:现场示例:
const courseContent = { quiz: { options: ["test1", "test2", "test3", "test4"], }, }; const quizResponseCountToRemove = 2; console.log("before", JSON.stringify(courseContent.quiz.options)); courseContent.quiz.options.length -= quizResponseCountToRemove; console.log("after", JSON.stringify(courseContent.quiz.options));
You can use slice
if you are looking to truncate an array.如果要截断数组,可以使用
slice
。 The problem with setting length
of the array is that the length
should be non-negative , so you need to add some checks.设置数组
length
的问题是length
应该是非负的,所以你需要添加一些检查。
In code snippet below even if delCount
is 200
, no additional checks are required slice
will simply return an empty array.在下面的代码片段中,即使
delCount
是200
,也不需要额外的检查slice
只会返回一个空数组。 But remember slice
returns a new array.但请记住
slice
返回一个新数组。
const arr = ["test1", "test2", "test3", "test4"], delCount = 2, newArr = arr.slice(0, -delCount); console.log(newArr)
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