whyy output showing : undefined undefined ( Java Script )

Question

function Book(title, author, isbn, stock, cost) {
  this.title = title;
  this.author = author;
  this.isbn = isbn;
  this.stock = stock;
  this.cost = cost;
  this.summary = function () {
    `${this.title} by ${this.author} (ISBN: ${this.isbn}) costs $ ${this.cost}`;
  };
  this.isAvailable = function () {
    this.stock > 0
      ? `${this.title} is available`
      : `${this.title} is not available at the moment`;
  };
}

const product = new Book(
  "The Design of Everyday Things",
  "Don Norman",
  "978 - 0 - 465 - 05571 - 5",
  10,
  17.99
);
console.log(product.summary());
console.log(product.isAvailable());

It has to print:

"The Design of Everyday Things by Don Norman (ISBN: 978 - 0 - 465 - 05571 - 5) costs $17.99"

"The Design of Everyday things is available"

You have to use return to get a result returned by a normal function call. — Christopher
– Christopher, Commented Dec 25, 2022 at 15:23
Use linters like ESLint or JSHint to find problems with your code immediately. Relevant linter warning: “Expected an assignment or function call and instead saw an expression.”. — Sebastian Simon
– Sebastian Simon, Commented Dec 25, 2022 at 15:28

Nora Söderlund · Accepted Answer · 2022-12-25 15:23:40Z

2

You're not returning anything in your functions:

function Book(title, author, isbn, stock, cost) {
  this.title = title;
  this.author = author;
  this.isbn = isbn;
  this.stock = stock;
  this.cost = cost;
  this.summary = function () {
    return `${this.title} by ${this.author} (ISBN: ${this.isbn}) costs $ ${this.cost}`;
  };
  this.isAvailable = function () {
    return this.stock > 0
      ? `${this.title} is available`
      : `${this.title} is not available at the moment`;
  };
}

const product = new Book(
  "The Design of Everyday Things",
  "Don Norman",
  "978 - 0 - 465 - 05571 - 5",
  10,
  17.99
);
console.log(product.summary());
console.log(product.isAvailable());

Using arrow functions, you can skip the return keyword if you prefer:

function Book(title, author, isbn, stock, cost) {
  this.title = title;
  this.author = author;
  this.isbn = isbn;
  this.stock = stock;
  this.cost = cost;
  this.summary = () =>
    `${this.title} by ${this.author} (ISBN: ${this.isbn}) costs $ ${this.cost}`;
  
  this.isAvailable = () =>
    this.stock > 0
      ? `${this.title} is available`
      : `${this.title} is not available at the moment`;
}

const product = new Book(
  "The Design of Everyday Things",
  "Don Norman",
  "978 - 0 - 465 - 05571 - 5",
  10,
  17.99
);
console.log(product.summary());
console.log(product.isAvailable());

answered Dec 25, 2022 at 15:23

Nora Söderlund

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1 Comment

dheerajSan Over a year ago

i have used : return ${this.title} by ${this.author} (ISBN: ${this.isbn}) costs $ ${this.cost}

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