Why is it possible to treat a primitive string as an object when accessing it in JavaScript?

In JavaScript, when accessing a primitive string string (not String), automatic conversion (boxing/wrapping) to a String object occurs. This temporary object contains methods and properties available for strings (e.g., .length, .toUpperCase(), .indexOf()). After the operation on this temporary object, it is destroyed.

For example:

// primitive string
const myString = "hello";

// Accessing the `.length` property on a primitive string
// Automatically wrapped into a String object { "hello" }
// Then the `.length` property is called on this temporary object
console.log(myString.length); // 5

// Calling the `.toUpperCase()` method on a primitive string
// Automatically wrapped into a String object { "hello" }
// Then the `.toUpperCase()` method is called on this temporary object
console.log(myString.toUpperCase()); // "HELLO"

// After the operation, the temporary object is destroyed.
// myString remains a primitive string.
console.log(typeof myString); // "string"

This behavior provides convenience when working with primitive types, allowing object-oriented syntax to access their functionality without explicitly creating wrapper objects.

Comparison of primitive string and String object:

Characteristic	Primitive string ("string")	String object (new String("string"))
Type	string	object
Comparison with ===	By value	By reference
General	More performant	Less performant
Usage	Preferable	Avoid unless explicitly needed