Introduction to JavaScript – Properties

Introduction to JavaScript – Properties

Understanding Instances and Properties

When you introduce a new piece of data into a JavaScript program, the browser saves it as an instance of a data type. An instance is an individual case (or object) of a data type.

For example, when you create a string like “Hello”, JavaScript saves it as an instance of the string data type in the computer’s memory. Similarly, the number 40.7 is stored as an instance of the number data type.

What Are Properties?

An instance, like the string “Hello”, has additional information attached to it. This additional information is called a property. Properties are values associated with a JavaScript object.

Every string instance has a property called length that stores the number of characters in it. You can retrieve property information by appending the string with a period and the property name.

Example:

            console.log('Hello'.length);
        

In the example above, the value saved to the length property is retrieved from the string “Hello”. The program prints 5 to the console because “Hello” has five characters in it.

More Examples of Properties – Introduction to JavaScript – Properties

Example 1: Accessing the length of different strings

            console.log('JavaScript'.length); // Output: 10
            console.log('Programming'.length); // Output: 11
            console.log('12345'.length);       // Output: 5
        

In these examples, the length property returns the number of characters in each string.

Example 2: Using properties with numbers

            let num = 40.7;
            console.log(Number.isInteger(num)); // Output: false
        

In this example, the isInteger method is used to check if num is an integer.

Using Properties in Objects – Introduction to JavaScript – Properties

In JavaScript, objects are collections of properties, and these properties are key-value pairs.

Example:

            let car = {
              make: 'Toyota',
              model: 'Corolla',
              year: 2021
            };

            console.log(car.make);  // Output: Toyota
            console.log(car.model); // Output: Corolla
            console.log(car.year);  // Output: 2021
        

In this example, the car object has three properties: make, model, and year. Each property holds a value that can be accessed using dot notation.

Assignment – Introduction to JavaScript – Properties

Create a JavaScript object called book with the following properties:

• title (a string)
• author (a string)
• pages (a number)
• publishedYear (a number)

Write code to log each property value to the console using dot notation.

Answer Key

            // Assignment solution
            let book = {
              title: 'JavaScript: The Good Parts',
              author: 'Douglas Crockford',
              pages: 176,
              publishedYear: 2008
            };

            console.log(book.title);         // Output: JavaScript: The Good Parts
            console.log(book.author);        // Output: Douglas Crockford
            console.log(book.pages);         // Output: 176
            console.log(book.publishedYear); // Output: 2008
        

In this solution, the book object is created with four properties: title, author, pages, and publishedYear. Each property value is logged to the console using dot notation.

By understanding instances and properties, you can effectively manipulate and access data in your JavaScript programs. Properties allow you to store and retrieve additional information about an instance, making your code more dynamic and powerful.

13: What are JavaScript Properties and Methods | Properties and Methods | JavaScript Tutorial – Introduction to JavaScript – Properties

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