Aprenda Manipulating Object Properties | Understanding and Working with Objects

When working with JavaScript objects, you often need to add, update, or remove properties to keep your data accurate and up-to-date. Understanding how to manipulate object properties is essential for dynamic applications, where the structure of your data can change during execution. You can add new properties to an object simply by assigning a value to a new property name, update existing properties by assigning a new value to an existing property, and remove properties with the delete operator.


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// Adding and updating properties
const user = {
  name: "Alice",
  age: 28
};

// Add a new property
user.email = "alice@example.com";

// Update an existing property
user.age = 29;

console.log(JSON.stringify(user));


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// Deleting properties
const product = {
  id: 101,
  name: "Book",
  price: 12.99
};

// Remove the price property
delete product.price;

console.log(JSON.stringify(product));

After manipulating properties, you may want to check whether a property exists on an object. JavaScript provides a couple of ways to do this: the in operator and the hasOwnProperty method.

The in operator checks if a property exists anywhere in the object's prototype chain;
The hasOwnProperty checks only for properties directly on the object itself. For example, after adding and deleting properties as shown above, you can use these checks to confirm the presence or absence of specific properties.


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const car = {
  make: "Toyota",
  model: "Corolla"
};

// Add a new property
car.year = 2018;

// Check property existence with 'in'
console.log("year" in car); // true
console.log("color" in car); // false

// Check property existence with hasOwnProperty
console.log(car.hasOwnProperty("model")); // true
console.log(car.hasOwnProperty("toString")); // false (inherited from prototype)

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Seção 1. Capítulo 3

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              12345678910111213
            
// Adding and updating properties
const user = {
  name: "Alice",
  age: 28
};

// Add a new property
user.email = "alice@example.com";

// Update an existing property
user.age = 29;

console.log(JSON.stringify(user));


              1234567891011
            
// Deleting properties
const product = {
  id: 101,
  name: "Book",
  price: 12.99
};

// Remove the price property
delete product.price;

console.log(JSON.stringify(product));

After manipulating properties, you may want to check whether a property exists on an object. JavaScript provides a couple of ways to do this: the in operator and the hasOwnProperty method.

The in operator checks if a property exists anywhere in the object's prototype chain;
The hasOwnProperty checks only for properties directly on the object itself. For example, after adding and deleting properties as shown above, you can use these checks to confirm the presence or absence of specific properties.


              123456789101112131415
            
const car = {
  make: "Toyota",
  model: "Corolla"
};

// Add a new property
car.year = 2018;

// Check property existence with 'in'
console.log("year" in car); // true
console.log("color" in car); // false

// Check property existence with hasOwnProperty
console.log(car.hasOwnProperty("model")); // true
console.log(car.hasOwnProperty("toString")); // false (inherited from prototype)

Tudo estava claro?

Obrigado pelo seu feedback!

Seção 1. Capítulo 3