🔰iterable
an object that can iterate over itself.
an object that can make iterators. (like Sequence in Swift, must implement .makeIterator() method)
for (const value of iterable) { ... } // for-of
[...iterable] // spread into array elements
f(...iterable) // spread into function arguments
const [a, b, c] = iterable; // destructuring iterable
Array.from(iterable) // iterable -> array(by default) object is not iterable❗
let obj = { x: 1, y: 2, z: 3 };
for (let value of obj) { } // ⛔ TypeError
// ⭐️ workarounds
for (let key of Object.keys(obj) { ... }
for (let key in obj) { ... } // for-in
for (let value of Object.values(obj) { ... }
for (let [key, value] of Object.entries(obj) { ... }use cases：
for (const item of iterable) { ... } // ⭐️ for-of loop
[...iterable] // ⭐️ spread into array elements
f(...iterable) // ⭐️ spread into function arguments
let [a, b, c] = iterable // ⭐️ iterable destructuring
// ⭐️ functios that accept iterables:
Array.from(iterable/array-like)
Promise.all(iterable)iterables：
Array, String, Set, Map, TypedArray,
objects returned by generator functions.
must implement the make-iterator method named [Symbol.iterator].
some iterables only iterate once❗️
an iterable can be infinite. ( 👉 see： *integers())
comforming to Iterable
make-iterator method - method named
[Symbol.iterator].Iterable+ext (extension) - extends iterables with custom methods.
obj.isIterable - check if an object is iterable.
💾 use cases
for (const value ofiterable)- for-of loop.[...iterable]- spread into array elements.f(...iterable)- spread into function arguments.const [a, b, c] =iterable;- iterable destructuring.Array.from(iterable)- convert to array.
special iterable
✨ examples：
range() - half-open range of numbers.
*integers() - generate infinite iterable.
ClosedRange - closed range of integers.
array-likes and iterables are different things.
destructuring assignment can be used with iterables.
defining iterable (using generator function)
const iterable = {
// ⭐️ "make-iterator" method
*[Symbol.iterator]() {
yield 1; yield 2; yield 3;
},
};more examples ...
*integers() - generate non-negative integers.
Sequence - sequence of numbers.
Array.from() - convert iterable / array-like to array.
iterable protocol ( = Sequence protocol in Swift )
Symbol.iterator ( = makeIterator in Swift )
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