在JavaScript中从数组中获取对象

Question

I have an array of objects (student objects which have properties like studentID , grade , dob , registeredDate ) and I have another array of objects (books objects which have properties studentID , bookID , bookISBN ).

It's a Web app for managing the library at a small school. What I want to do is that when a book (say has title Welcome Home ) has been borrowed by student with studentID 4, when you try to lend that book (of course a copy since the library can have a number of them in stock) to someone else, the student with studentID 4 shouldn't be available in the list of students who are eligible to get that book (unless if the student had returned the book first).

The booksList Array is like below:

[
{
bookEdition: "2nd edition",
bookISBN: 9876533278765,
bookStatus: 0,
bookTitle: "Real Machines",
dateTaken: "2018-10-28",
returnDate: "2018-11-27",
studentID: "0000003"
},

{
bookEdition: "2015 edition",
bookISBN: 9876532226712,
bookStatus: 0,
bookTitle: "Real Machines",
dateTaken: "2018-08-28",
returnDate: "2018-09-27",
studentID: "0000004"
}
];

The studentsList is as below:

[
{
bio: "Needs extra work. Has problems with mathematics",
birthday: "2005-05-12",
className: "grade 5",
fullname: "Bridget Friday",
gender: "Female",
parentName: "Josam Friday",
studentID: "0000003",
studentStatus: "approved"
}, 

{
bio: "A bit naughty but intelligent. Pay close attention to his diet.",
birthday: "2003-11-07",
className: "grade 6",
fullname: "Charles Ben",
gender: "Male",
parentName: "Chris Ben",
studentID: "0000004",
studentStatus: "approved"
}
];

Now, I was trying to use the filter function but it doesn't give me the results I want. The thing that links the two array objects and the objects in them is the studentID .

I tried

var legitStudents = studentsList.filter(el => {
  return !booksList.includes(el.studentID);
});

The above doesn't work. The arrays ( studentList and booksList ) are fetched dynamically and I can't tell which studentID s are in booksList .

How can I get this to work as I want them?

Answer 1

return !booksList.includes(el.studentID);

should be

return !booksList.map(i => i.studentID).includes(el.studentID);

As a couple people said in the comments of your question, the problem is your code is expecting booksList to be an array of studentID s. Since it's actually a list of books that have been checked out by students, you first need to make an array of all studentID s in booksList then you can use includes on the resulting array. See map .

Answer 2

You can use Rocky Sims' solution or you can try this as well

var legitStudents = studentList.filter(student => {
  return !booksList.filter(book => book.studentID === student.studentID).length;
});