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Vitalii Telychko
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fix
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‎ES6/Array_features/methods.js

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// 1. Array.from
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// const spans = document.querySelectorAll('span.name');
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//
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// // map(), generically:
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// const names1 = Array.prototype.map.call(spans, s => s.textContent);
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//
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// // Array.from():
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// const names2 = Array.from(spans, s => s.textContent);
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// function f() {
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// const instanceOfArray = Array.from(arguments, x => x * 3);
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// console.log(instanceOfArray);
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// }
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//
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// f(1, 2, 3);
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// 2. Array.of
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// const arr = Array.of(1, 'hello', false, { a: 2 });
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// console.log(arr instanceof Array);
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// 3. Array.prototype.entries()
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// Array.from(['a', 'b'].keys()) => [ 0, 1 ]
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// 4. Array.prototype.keys()
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// Array.from(['a', 'b'].values()) => [ 'a', 'b' ]
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// 5. Array.prototype.entries()
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// Array.from(['a', 'b'].entries()) => [ [ 0, 'a' ], [ 1, 'b' ] ]
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// [...['a', 'b'].keys()] => via spread operator
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// for (const [index, element] of ['a', 'b'].entries()) {
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// console.log(index, element);
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// }
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// 6. Array.prototype.find(predicate, thisArg?)
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// 7. Array.prototype.findIndex(predicate, thisArg?)
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// [NaN].findIndex(y => Object.is(NaN, y))
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// 8. Array.prototype.copyWithin()
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// const arr = [0, 1, 2, 3, 4, 5];
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// arr.copyWithin(3, 3, 5);
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// console.log(arr);
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// 9. Array.prototype.fill()
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// const arr = ['a', 'b', 'c'];
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// arr.fill(7)
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// [ 7, 7, 7 ]
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// Restrict
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// ['a', 'b', 'c'].fill(7, 1, 2); // [ 'a', 7, 'c' ]
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// Treat holes like undefined
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// Array.from(['a',,'b']); // [ 'a', undefined, 'b' ]
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/*
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forEach(), filter(), every() and some() ignore holes.
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map() skips but preserves holes.
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join() and toString() treat holes as if they were undefined elements, but interprets both null and undefined as empty strings.
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copyWithin() creates holes when copying holes (i.e., it deletes elements if necessary).
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entries(), keys(), values() treat each hole as if it was the element undefined.
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find() and findIndex() do the same.
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fill() doesn’t care whether there are elements at indices or not.
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*/

‎ES6/Iterables_iterators/examples.js

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// function objectEntries(obj) {
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// let it = Reflect.ownKeys(obj)[Symbol.iterator]();
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// return {
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// [Symbol.iterator]() {
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// return this;
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// },
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// next() {
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// let { done, value: key } = it.next();
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// if(done) {
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// return { done: true };
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// }
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// return { value: obj[key] };
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// }
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// }
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// }
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//
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// // objectEntries({ a: 1, b: 2 });
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//
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// for(const x of objectEntries({ a: 1, b: 2 })) {
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// console.log(x);
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// }
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// Combinators are functions that combine existing iterables to create new ones.
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// function take(n, iterable) {
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// const it = iterable[Symbol.iterator]();
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// return {
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// [Symbol.iterator]() {
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// return this;
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// },
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// next() {
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// if(n > 0) {
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// n--;
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// return it.next();
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// } else {
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// return { done: true }
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// }
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// }
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// }
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// }
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//
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// const arr = ['a', 'b', 'c', 'd'];
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// for (const x of take(2, arr)) {
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// console.log(x);
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// }
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// function zip(...iterables) {
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// const iterators = iterables.map(i => i[Symbol.iterator]());
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// let done = true;
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// return {
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// [Symbol.iterator]() {
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// return this;
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// },
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// next() {
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// if(!done) {
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// const items = iterators.map(i => i.next());
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// done = items.some(item => item.done);
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// if (!done) {
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// return { value: items.map(i => i.value) };
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// }
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// for (const iterator of iterators) {
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// if (typeof iterator.return === 'function') {
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// iterator.return();
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// }
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// }
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// }
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// return { done: true };
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// }
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// }
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// }
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//
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// const zipped = zip(['a', 'b', 'c'], ['d', 'e', 'f']);
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//
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// for(const x of zipped) {
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// console.log(x);
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// }

‎ES6/Iterables_iterators/implementing_details.js

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// 1. Custom iterator
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// const iterables = {
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// [Symbol.iterator]() {
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// let step = 0;
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// return {
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// next() {
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// if(step <= 2) {
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// step++;
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// }
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// switch (step) {
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// case 1:
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// return { value: 'hello', done: false };
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// case 2:
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// return { value: 'world', done: false };
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// default:
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// return { value: undefined, done: true };
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// }
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// }
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// };
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// }
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// };
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//
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// for(const x of iterables) {
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// console.log(x);
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// }
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// 2. Iterate Object with properties
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// function objectEntries(obj) {
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// let index = 0;
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//
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// // In ES6, you can use strings or symbols as property keys,
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// // Reflect.ownKeys() retrieves both
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// const propKeys = Reflect.ownKeys(obj);
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//
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// return {
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// [Symbol.iterator]() {
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// return this;
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// },
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// next() {
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// if (index < propKeys.length) {
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// const key = propKeys[index];
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// index++;
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// return { value: [key, obj[key]] };
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// } else {
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// return { done: true };
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// }
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// }
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// };
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// }
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//
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// const obj = { first: 'Jane', last: 'Doe' };
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// for (const [key,value] of objectEntries(obj)) {
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// console.log(`${key}: ${value}`);
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// }

‎ES6/Iterables_iterators/iterable_data_source.js

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// Arrays
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// for (const x of ['a', 'b']) {
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// console.log(x);
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// }
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// Strings
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// for (const x of 'a\uD83D\uDC0A') {
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// console.log(x);
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// }
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/*
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You have just seen that primitive values can be iterable. A value doesn’t have to be an object in order to be iterable.
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That’s because all values are coerced to objects before the iterator method (property key Symbol.iterator) is accessed.
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*/
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// Maps
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// const map = new Map().set('a', 1).set('b', 2);
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// for (const pair of map) {
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// console.log(pair);
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// }
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// Sets
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// const set = new Set().add('a').add('b');
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// for (const x of set) {
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// console.log(x);
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// }
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// Note that WeakMaps and WeakSets are not iterable.
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// arguments
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// function printArgs() {
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// for (const x of arguments) {
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// console.log(x);
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// }
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// }
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// DOM data structures
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// for (const node of document.querySelectorAll('div')) {
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// ···
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// }
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// Plain objects are not iterable
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// for (const x of {}) { // TypeError
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// console.log(x);
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// }
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// just ...
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// const obj = { first: 'Jane', last: 'Doe' };
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//
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// for (const [key,value] of objectEntries(obj)) {
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// console.log(`${key}: ${value}`);
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// }

‎ES6/Iterables_iterators/iterating_constructs.js

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/*
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The following ES6 language constructs make use of the iteration protocol:
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Destructuring via an Array pattern
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for-of loop
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Array.from()
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Spread operator (...)
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Constructors of Maps and Sets
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Promise.all(), Promise.race()
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yield*
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*/
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// 1. Via Array patterns
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// const set = new Set().add('a').add('b').add('c');
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//
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// const [x,y] = set;
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// // x='a'; y='b'
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//
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// const [first, ...rest] = set;
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// // first='a'; rest=['b','c'];
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// 2. The for-of loop
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// for (const x of iterable) {
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// ···
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// }
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// 3. Array.from()
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// > Array.from(new Map().set(false, 'no').set(true, 'yes'))
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// [[false,'no'], [true,'yes']]
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// > Array.from({ length: 2, 0: 'hello', 1: 'world' })
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// ['hello', 'world']
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// 4. Spread operator
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// > const arr = ['b', 'c'];
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// > ['a', ...arr, 'd']
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// ['a', 'b', 'c', 'd']
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// 5. Maps and Sets
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// 6. Promises - all | race
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// 7. yield*
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// function* yieldAllValuesOf(iterable) {
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// yield* iterable;
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// }

‎ES6/Iterables_iterators/overview.js

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/*
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An iterable is a data structure that wants to make its elements accessible to the public.
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It does so by implementing a method whose key is Symbol.iterator.
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That method is a factory for iterators.
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An iterator is a pointer for traversing the elements of a data structure (think cursors in databases).
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*/
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// Iterable values - Arrays, Strings, Maps, Sets, DOM data structures (work in progress)
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/*
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Source: A value is considered iterable if it has a method whose key is the symbol Symbol.iterator
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that returns a so-called iterator. The iterator is an object that returns values via its method next().
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We say: it iterates over the items (the content) of the iterable, one per method call.
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*/
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// Example
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const arr = ['a', 'b', 'c'];
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const it = arr[Symbol.iterator]();
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it.next();
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it.next();
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it.next();
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/*
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Iterable and iterators are part of a so-called protocol (interfaces plus rules for using them) for iteration.
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A key characteristic of this protocol is that it is sequential: the iterator returns values one at a time.
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That means that if an iterable data structure is non-linear (such as a tree), iteration will linearize it.
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*/

‎ES6/Parameter_handling/tips.js

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function mandatory() {
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throw new Error('Missing parameter');
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}
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function foo(mustBeProvided = mandatory()) {
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return mustBeProvided;
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}
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// function mandatory() {
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// throw new Error('Missing parameter');
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// }
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// function foo(mustBeProvided = mandatory()) {
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// return mustBeProvided;
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// }

‎index.html

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<div id="content"></div>
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<script src="programming_paradigms/functional_programming/reduce.js"></script>
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<script src="ES6/Array_features/methods.js"></script>
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</body>
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</html>

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