TypeError: Spread syntax requires ...iterable[Symbol.iterator] to be a function (V8-based & Safari)TypeError: %Array%.from requires that the property of the first argument, items[Symbol.iterator], when exists, be a function (V8-based & Safari)TypeError: Array.fromAsync requires that the property of the first argument, items[Symbol.asyncIterator], when exists, be a function (V8-based & Safari)TypeError: object is not iterable (cannot read property Symbol(Symbol.iterator)) (V8-based)TypeError: x is not async iterable (V8-based)TypeError: x is not iterable (V8-based & Firefox)TypeError: undefined is not a function (near '...y of x...') (Safari)TypeError: Array.from: no function (Safari)TypeError: Type error (Safari)

The value which isspread into an array or function call, given as the right-hand side offor...of,or as argument of a function such asPromise.all orSet(),or as the source of an arraydestructuring pattern,is not aniterable object.An iterable can be a built-in iterable type such asArray,String orMap, a generator result, oran object implementing theiterable protocol.

const nonIterable1 = {};const nonIterable2 = { [Symbol.iterator]: 1 };[...nonIterable1];Math.max(...nonIterable1);for (const x of nonIterable1);new Set(nonIterable1);Array.from(nonIterable2);new Int8Array(nonIterable2);const [] = nonIterable1;

const myObj = { arrayOrObjProp1: {}, arrayOrObjProp2: [42] };const {  arrayOrObjProp1: [value1],  arrayOrObjProp2: [value2],} = myObj; // TypeError: object is not iterableconsole.log(value1, value2);

The non-iterable might turn to beundefined in some runtime environments.

In JavaScript,Objects are not iterable unless they implementtheiterable protocol.Therefore, you cannot usefor...ofto iterate over the properties of an object.

const obj = { France: "Paris", England: "London" };for (const p of obj) {  // …} // TypeError: obj is not iterable

Instead you have to useObject.keys orObject.entries, toiterate over the properties or entries of an object.

const obj = { France: "Paris", England: "London" };// Iterate over the property names:for (const country of Object.keys(obj)) {  const capital = obj[country];  console.log(country, capital);}for (const [country, capital] of Object.entries(obj)) {  console.log(country, capital);}

Another option for this use case might be to use aMap:

const map = new Map();map.set("France", "Paris");map.set("England", "London");// Iterate over the property names:for (const country of map.keys()) {  const capital = map.get(country);  console.log(country, capital);}for (const capital of map.values()) {  console.log(capital);}for (const [country, capital] of map.entries()) {  console.log(country, capital);}

Generator functionsare functions you call to produce an iterable object.

function* generate(a, b) {  yield a;  yield b;}for (const x of generate) {  console.log(x);} // TypeError: generate is not iterable

When they are not called, theFunction object corresponding to thegenerator is callable, but not iterable. Calling a generator produces an iterableobject which will iterate over the values yielded during the execution of thegenerator.

function* generate(a, b) {  yield a;  yield b;}for (const x of generate(1, 2)) {  console.log(x);}

Custom iterables can be created by implementing theSymbol.iterator method. You must be certain that your iterator methodreturns an object which is an iterator, which is to say it must have a next method.

const myEmptyIterable = {  [Symbol.iterator]() {    return []; // [] is iterable, but it is not an iterator — it has no next method.  },};Array.from(myEmptyIterable); // TypeError: myEmptyIterable is not iterable

Here is a correct implementation:

const myEmptyIterable = {  [Symbol.iterator]() {    return [][Symbol.iterator]();  },};Array.from(myEmptyIterable); // []

• Iterable protocol
• Object.keys
• Object.entries
• Map
• Generator functions
• for...of