Let's understand iteration in js by making Range class.
class Range {
constructor(start,end) {
this.start = start
this.end = end
}
[Symbol.iterator]() {
let i = this.start
return {
next: () => {
if (i > this.end) {
return {value: undefined, done: true}
}
return {value: i++, done: false}
}
}
}
}
const r = new Range(1,10)
for (let i of r) {
console.log(i)
}
console.log("finished")
Range class here is an iterable because it follows the iterable protocol. It's Symbol.iterator method returns an object which follows the iterator protocol.
An object is said to be following the iterator protocol when it implements the next method. It's next method should return an object which conforms to the IteratorResult interface.