Iterable

Iteration protocols are a set of protocols (like Interfaces) to be implemented by a Prototype.

Iterable

An Iterable is something which can be iterated over. There are a few built-in iterables such as Arrays, Strings, and Sets.

An Object is not an iterable.

const name = "Jeffrey";

for (const char of name) {
	// "J" "e" "f" "f" "r" "e" "y"
	console.log(char);
};

// [ "J", "e", ..., "y" ]
const chars = [...name];

for...of vs for...in

for...of iterates over items in an iterable. for...in enumerates over properties in an Object.

Think of for...in as an alias for for...of iterable.keys()

const numbers = [ 1, 2, 3, 4 ];
for (const num of numbers) { /* 1, 2, 3, 4 */ };
for (const index in numbers) { /* 0, 1, 2, 3 */ };

const numberMap = { one: 1, two: 2, three: 3, four: 4 };
for (const num in numberMap) {
	// "one", "two", "three", "four"
};