04 - Methods

Methods of Primitives

JavaScript supports an object-oriented programming style. This means that rather than having globally defined functions to operate on values of various types, the types themselves define methods for working with values.

To sort the elements of an array a, we don’t pass a to a sort() function. Instead, we invoke the sort() method of a:

a.sort();
// The object-oriented version of sort(a).

Technically, it is only JavaScript objects that have methods. Numbers, strings, booleans, and symbol values behave as if they have methods. In JavaScript, null and undefined are the only values that methods cannot be invoked on.

While primitives (like strings, numbers, booleans) are not objects by themselves, JavaScript allows them to behave like objects in certain situations. This is done through “wrapper objects” that temporarily convert the primitive to an object for method access.

When you call a method on a primitive value, JavaScript wraps the primitive in an appropriate object wrapper (e.g., String, Number, Boolean, Symbol, or BigInt). After the method call, the wrapper is discarded.

let str = "hello";
console.log(str.toUpperCase());  // "HELLO"

• str is a primitive string.
• JavaScript temporarily wraps it in a String object to call the toUpperCase method, and then the wrapper is discarded. So primitives can provide methods yet still remain lightweight.

Wrappers for Each Primitive Type:

• String has methods like .toUpperCase(), .toLowerCase(), etc.
• Number has methods like .toFixed(), .toPrecision(), etc.
• Boolean has methods like .toString() to convert it into a string.

However, null and undefined do not have object wrappers, so they cannot be used with methods.

Converting Primitive Types:

let num = Number("123"); // Converts the string "123" into a number
let booleanVal = Boolean(0); // Converts 0 to false

Note: null and undefined do not have methods because they are the most primitive types and do not have associated object wrappers.

• Primitive types: Single values, immutable, include string, number, boolean, null, undefined, symbol, bigint.
• Reference types: Store collections of data and more complex entities, include object, array, function, etc.
• typeof operator: Used to check the type of a value.
• Wrapper objects: Allow primitives to behave like objects when methods are invoked on them (e.g., String, Number, Boolean).

Empty Values

• null is used to assign an empty, nothing, or unknown value to a variable.
• undefined means the value is not assigned. It is the default initial value when a variable is declared but the value is not assigned.

Many operations yield undefined when they don’t produce a meaningful value.

null and undefined are used to denote the absence of a meaningful value or when the value is unknown. These two are values but carry no information. Both are mostly interchangeable.