50 hints JS(ES6) developer must know (5th part)

const numbers = [1, 2, 3, 4, 5];// badlet sum = 0;for (let num of numbers) {  sum += num;}sum === 15;// goodlet sum = 0;numbers.forEach((num) => {  sum += num;});sum === 15;// best (use the functional force)const sum = numbers.reduce((total, num) => total + num, 0);sum === 15;// badconst increasedByOne = [];for (let i = 0; i < numbers.length; i++) {  increasedByOne.push(numbers[i] + 1);}// goodconst increasedByOne = [];numbers.forEach((num) => {  increasedByOne.push(num + 1);});// best (keeping it functional)const increasedByOne = numbers.map((num) => num + 1);

// badfunction * foo() {  // ...}// badconst bar = function * () {  // ...};// badconst baz = function *() {  // ...};// badconst quux = function*() {  // ...};// badfunction*foo() {  // ...}// badfunction *foo() {  // ...}// very badfunction*foo() {  // ...}// very badconst wat = function*() {  // ...};// goodfunction* foo() {  // ...}// goodconst foo = function* () {  // ...};

const luke = {  jedi: true,  age: 28,};// badconst isJedi = luke['jedi'];// goodconst isJedi = luke.jedi;

const luke = {  jedi: true,  age: 28,};function getProp(prop) {  return luke[prop];}const isJedi = getProp('jedi');

// badconst binary = Math.pow(2, 10);// goodconst binary = 2 ** 10;

// badsuperPower = new SuperPower();// goodconst superPower = new SuperPower();

// badconst items = getItems(),    goSportsTeam = true,    dragonball = 'z';// bad// (compare to above, and try to spot the mistake)const items = getItems(),    goSportsTeam = true;    dragonball = 'z';// goodconst items = getItems();const goSportsTeam = true;const dragonball = 'z';

// badlet i, len, dragonball,    items = getItems(),    goSportsTeam = true;// badlet i;const items = getItems();let dragonball;const goSportsTeam = true;let len;// goodconst goSportsTeam = true;const items = getItems();let dragonball;let i;let length;

// bad - unnecessary function callfunction checkName(hasName) {  const name = getName();  if (hasName === 'test') {    return false;  }  if (name === 'test') {    this.setName('');    return false;  }  return name;}// goodfunction checkName(hasName) {  if (hasName === 'test') {    return false;  }  const name = getName();  if (name === 'test') {    this.setName('');    return false;  }  return name;}

// bad(function example() {  // JavaScript interprets this as  // let a = ( b = ( c = 1 ) );  // The let keyword only applies to variable a; variables b and c become  // global variables.  let a = b = c = 1;}());console.log(a); // throws ReferenceErrorconsole.log(b); // 1console.log(c); // 1// good(function example() {  let a = 1;  let b = a;  let c = a;}());console.log(a); // throws ReferenceErrorconsole.log(b); // throws ReferenceErrorconsole.log(c); // throws ReferenceError// the same applies for `const`

// badconst array = [1, 2, 3];let num = 1;num++;--num;let sum = 0;let truthyCount = 0;for (let i = 0; i < array.length; i++) {  let value = array[i];  sum += value;  if (value) {    truthyCount++;  }}// goodconst array = [1, 2, 3];let num = 1;num += 1;num -= 1;const sum = array.reduce((a, b) => a + b, 0);const truthyCount = array.filter(Boolean).length;

// badconst foo =  superLongLongLongLongLongLongLongLongFunctionName();// badconst foo  = 'superLongLongLongLongLongLongLongLongString';// goodconst foo = (  superLongLongLongLongLongLongLongLongFunctionName());// goodconst foo = 'superLongLongLongLongLongLongLongLongString';

// badvar some_unused_var = 42;// Write-only variables are not considered as used.var y = 10;y = 5;// A read for a modification of itself is not considered as used.var z = 0;z = z + 1;// Unused function arguments.function getX(x, y) {    return x;}// goodfunction getXPlusY(x, y) {  return x + y;}var x = 1;var y = a + 2;alert(getXPlusY(x, y));// 'type' is ignored even if unused because it has a rest property sibling.// This is a form of extracting an object that omits the specified keys.var { type, ...coords } = data;// 'coords' is now the 'data' object without its 'type' property.