JS⟩ syntax ⟩ for loops ⟩ for-of ⟩ arrays are iterated "live"❗️
changes made during the iteration may affect the outcome of the iteration.
const _Number = require('./ext/Number_ext'); // for `num.isEven`
let [arr1, arr2, arr3] = [
[1, 2, 3],
[1,
2
,
3
]
,
[1, 2, 3],
];
let [count1, count2, count3] = [0, 0, 0];
// ---------------------------------
// ⭐ arrays are iterated "live"❗
// ---------------------------------
// ⭐ 1. append elements
for (const value of arr1) {
log(value); // 1,1,1,1,2,3❗
if (count1 < 3) arr1.unshift(count1); // ⭐ prepend element
count1++;
}
// ┌─── next
// 1, 2, 3
// ┌─── next
// 0, 1, 2, 3
// ┌─── next
// 1, 0, 1, 2, 3
// ┌─── next
// 2, 1, 0, 1, 2, 3
// ┌─── next
// 2, 1, 0, 1, 2, 3
// ┌─── next
// 2, 1, 0, 1, 2, 3
arr1, // [ 2, 1, 0, 1, 2, 3 ]❗
// ⭐ 2. prepend/append
for (const value of arr2) {
log(value); // 1,1,2,2,3,1❗
if (count2 < 3) count2.isEven
? arr2.unshift(count2) // ⭐ prepend new element
: arr2.push(count2); // ⭐ append new element
count2++;
}
// ┌─── next
// 1, 2, 3
// ┌─── next
// 0, 1, 2, 3
// ┌─── next
// 0, 1, 2, 3, 1
// ┌─── next
// 2, 0, 1, 2, 3, 1
// ┌─── next
// 2, 0, 1, 2, 3, 1
// ┌─── next // iteration ended
// 2, 0, 1, 2, 3, 1
arr2, // [ 2, 0, 1, 2, 3, 1 ]❗
// ⭐ 3. shift (remove first) element
for (const value of arr3) {
log(`value = ${value}`); // 1,3❗
if (count3 < 3) log(`shifted value: ${arr3.shift()}`); // ⭐ remove first element
count3++;
}
// ┌─── next
// 1, 2, 3 // iteration started (1 will be removed)
// ┌─── next
// 2, 3 // iteration ended (2 will be removed)
// 3, // (2 removed)
arr3, // [ 3 ]❗