Iterate array items

For-of

Iterate over “values” in the given array

const array1 = ["one", "two", "three"];
for (let entry of array1) {
  console.log(entry);
  // "one"
  // "two"
  // "three"
}

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For-in

Iterate over “keys” in the given array

const array2 = ["one", "two", "three"];
for (let entry in array2) {
  console.log(entry, typeof entry);
  // "0" "string"
  // "1" "string"
  // "2" "string"
}

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Iterate key-value

The .entries() method returns a new Array Iterator object that contains the key/value pairs for each index in the array.

const array3 = ["one", "two", "three"];
for (let [key, value] of array3.entries()) {
  console.log(key, value, typeof key, typeof value);
  // 0,  "one",  "number",  "string"
  // 1,  "two",  "number",  "string"
  // 2,  "three",  "number",  "string"
}

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Objects

For-of

To have the same approach as for an array, use Object.values() to iterate over values

const obj1 = { one: 10, two: 20, three: 30 };
for (let v of Object.values(obj1)) {
  console.log(v);
  // 10
  // 20
  // 30
}

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For-in

Same as for arrays, iterate over keys

const obj2 = { one: 10, two: 20, three: 30 };
for (let k in obj2) {
  console.log(k);
  // "one"
  // "two"
  // "three"
}

Can be used Object.keys() to transform obejct keys into the array and later can be iterated with for-of

Iterate key-value

Objects dont have function entries, but it is available via: Object.entries(<object>)

const obj3 = { one: 10, two: 20, three: 30 };
for (let [k, v] of Object.entries(obj3)) {
  console.log(k, v, typeof k, typeof v);
  // "one", 10,  "number",  "string"
  // "two", 20,  "number",  "string"
  // "three", 30,  "number",  "string"
}

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