Wie bekomme ich JavaScript um zu erkennen, ob ein Objekt in einem Array ist?

Question

Neu bei JavaScript-Objekten. Im folgenden Code kann ich eine Liste von Buchobjekten erstellen und ausfüllen, die jede Person "ausgecheckt" hat. Allerdings kann ich die Bücher nicht "zurückgeben", weil ich nicht erkennen kann, in welchem ​​Feld des Benutzers das Buch "ausgecheckt" ist. Ich verwende

if (Objekt im Array). . .

Ich habe dies aus einer der vorherigen Antworten. Der Anweisungsblock mit dem if wird nie ausgeführt. Danke für Ihre Hilfe!

function Book(title, pub_date, call_number, authors){ 
    this.title = title; 
    this.availability = true; 
    this.pub_date = pub_date; 
    this.current_date = null; 
    this.check_out_date = null; 
    this.call_number = call_number; 
    this.authors = authors; 
} 
Book.prototype.checkOut = function(){ 
     this.availability = false; 
     var rdom = (Math.random() * 31 +1).toFixed(0); 
     var current_date = new Date(); 
     this.check_out_date = new Date(current_date - rdom*24*3600*1000); 
    } 

Book.prototype.checkIn = function(){ 
     this.availability = true; 
    } 

Book.prototype.isOverdue = function(){ 
     var current_date = new Date(); 
     if ((current_date - this.check_out_date)/1000/3600/24 > 14) 
      return true; 
     else 
      return false; 
    } 

function Author(first_name, last_name){ 
    this.first_name = first_name; 
    this.last_name = last_name; 
} 

function Patron(firstname, lastname, lib_card){ 
    this.firstname = firstname; 
    this.lastname = lastname; 
    this.lib_card = lib_card; 
    this.books_out = []; 
    this.fine = 0; 
} 
Patron.prototype.readBook = function(book){ 
     this.books_out.push(book); 
    } 

Patron.prototype.returnBook = function(book){ 
     this.books_out.pop(book); 
    } 

var redAuthors, blueAuthors, greenAuthors, yellowAuthors, purpleAuthors 
var redAuthor1 = new Author('John', 'Smith'); 
var redAuthor2 = new Author('James', 'Sullivan'); 
var redAuthors = [redAuthor1, redAuthor2]; 
var blueAuthors = greenAuthors = yellowAuthors = purpleAuthors = redAuthors; 

redBook = new Book('Lakes', 1963, 456789, redAuthors); 
blueBook = new Book('Rivers', 1964, 123456, blueAuthors); 
greenBook = new Book('Streams', 1965, 234567, greenAuthors); 
yellowBook = new Book('Ponds', 1966, 345678, yellowAuthors); 
purpleBook = new Book('Brooks', 1967, 567891, purpleAuthors); 
var catalog = [redBook, blueBook, greenBook, yellowBook, purpleBook] 

var patron1 = new Patron('Sally', 'Hudson', '1'); 
var patron2 = new Patron('Rachel', 'Hung', '2'); 
var patron3 = new Patron('Andy', 'Cunningham', '3'); 
var patron4 = new Patron('Steve', 'Cote', '4'); 
var patron5 = new Patron ('Ted', 'Mitrou', '5'); 
var patrons = [patron1, patron2, patron3, patron4, patron5] 

for (var day_count = 0; day_count < 10; day_count++){ 
    for (var book_count = 0; book_count < 5; book_count++){ 
     if (catalog[book_count].availability == true){ 
      for (var pat_count = 0; pat_count < 5; pat_count++){ 
       if (patrons[pat_count].books_out.length <= 1){ 
        catalog[book_count].checkOut(); 
        patrons[pat_count].readBook(catalog[book_count]); 
        break; 
       } 
       else 
        continue; 
      } 
     } 
     else { 
      catalog[book_count].checkIn(); 
      for (pat_counter = 0; pat_counter < 5; pat_counter++){ 
       if (catalog[book_count] in patrons[pat_counter].books_out){ 
        if (catalog[book_count].isOverdue) 
         patrons[pat_counter].fine += 5; 
        patrons[pat_counter].books_out.returnBook(catalog[book_count]); 
       } 
      } 
     }  
    } 
} 

for (var k = 0; k < 5; k++){ 
    console.log("Patron: " + patrons[k].firstname + " " + patrons[k].lastname); 
    console.log("Books checked out: ") 
    for (l = 0; l < patrons[k].books_out.length; l++) { 
     console.log(patrons[k].books_out[l].title); 
    } 
    console.log("Fine: $" + patrons[k].fine); 
    console.log(); 
}  

Answer 1

können Sie indexOf verwenden:

if (array.indexOf(object) > -1) 

x in y nur true wenn x ist eine Zeichenkette, die den Namen einer Eigenschaft auf y zurückkehren würde.