For learning purposes I've created a JS-File. I implemented a Method inside the JS-Object to get a BookStorage counter. The thing is everytime I add Books the Browser gives me back the default value for the Object. Anyone have an Idea?
Here is some snippets of my Code:
Book-Class:
class Book{
constructor(
name,
quantity
){
this.name = name,
this.quantity = quantity
}
showStorage(param) {
if(param != null){
return this.quantity + param;
this.quantity += param;
}
else {return this.quantity;}
}
}
Main-Script:
import Book from "./Book.js"
const lordOfRings = new Book(
"Lord of the Rings",
10
)
console.log("The Book:", lordOfRings.name);
console.log("The number in Storage:", lordOfRings.showStorage());
console.log("Adding 10 Books to storage:", lordOfRings.showStorage(10));
console.log("Adding 10 Books to storage:", lordOfRings.showStorage());
console.log("New Storage amount of Books:", lordOfRings.showStorage(10));
My expected output was:
"Lord of the Rings"
10
20
20
30
Instead of that I get:
"Lord of the Rings"
10
20
10
20
The problem is because in a function, the return should be the last line.
The return statement ends function execution and specifies a value to be returned to the function caller. (MDN Docs)
Since the function execution ends, it means the code after the return statement is never executed.
I recommend debugging your code using a code execution visualizer
Here's part of your code. You tried to change the value of this.quantity after the return statement.
showStorage(param) {
if(param != null){
return this.quantity + param; // This doesn't change the value of this.quantity. It just returns that value + 10 (in your example). The value of `this.quantity` is always the same.
// This line does not run because it's after the return statement
this.quantity += param;
}
else {return this.quantity;}
}
}
Here's a minimal fix. You need to increment the value of this.quantity, then return it.
showStorage(param) {
if(param != null){
this.quantity += param;
return this.quantity;
}
else {return this.quantity;}
}
}
Here's a refactor taking into account comments from Ivar and Cristian Traìna
showStorage(param) {
if(param){ // an empty `param` is `undefined`, not `null` as the commenter said above.
this.quantity += param;
}
return this.quantity;
}