Bracket notation

Did you notice something unusual in the example of working with the dictionary?

var catsFavoriteFood = {
  Muffin: 'fish',
  Rudolph: 'cutlet',
  Snowball: 'milk'
};

var printFavoriteFood = function (name) {
  return 'My favorite food is ' + catsFavoriteFood[name];
};

console.log (printFavoriteFood ('Snowball'));
// Logs 'My favorite food is milk'

Before, we accessed the properties of an object using a fullstop, and in this example, we work with an object as an array, we read the property using square brackets: catsFavoriteFood[name]. Yes, that’s also possible. The method with brackets is called bracket notation, the method with a dot dot notation. Programmers are so original, right?

Bracket notation is much more flexible than dot notation. For example, you can read from an object a property whose name is written to a variable:

var name = 'Muffin';
var catsFavoriteFood = {Muffin: 'fish'};

console.log(catsFavoriteFood.name);
// Logs undefined in the console

console.log(catsFavoriteFood[name]);
// Logs 'fish' in the console

The first message contains undefined, because the object does not have the name property. The second message contains the required value, because the program understands that there is a variable inside the brackets. The value of the variable is placed in the brackets, and then the required property of the object will be found.

console.log(catsFavoriteFood[name]);
// Inside the program quietly turns into:
console.log(catsFavoriteFood['Muffin']);

And one more surprise: any strings, even strings with spaces, can be used as keys in an object. Such properties cannot be read with dot notation, but you can definitely do it with no problem with bracket notation.

var cat = { 'favorite food': 'Milk' };

console.log(cat.favorite food);
// Causes an error

console.log(cat ['favorite food']);
// Works fine

By the way, why did we take the dictionaries out of the function to the very beginning of the program? Values ​​that are stored in these objects do not depend on the parameters of the function or computer object. These are the rules that apply to the whole program. They can be used in other functions and operations, if necessary. If the dictionaries were in the body of the function, they would be created only when the function was called.

Why does this even work? The object inside the function sees objects that are declared at the very beginning of the program. This is how scopes work. We will analyze this language feature later on, in other courses.

Now that the dictionaries have been created, and we learned how to work with them, we can calculate the price of the computer in one line. We will use the getPrice method. We will override it by adding new calculations.