50 hints JS(ES6) developer must know (8th part)

// badconst story = [    once  , upon  , aTime];// goodconst story = [  once,  upon,  aTime,];// badconst hero = {    firstName: 'Ada'  , lastName: 'Lovelace'  , birthYear: 1815  , superPower: 'computers'};// goodconst hero = {  firstName: 'Ada',  lastName: 'Lovelace',  birthYear: 1815,  superPower: 'computers',};

// bad - git diff without trailing commaconst hero = {     firstName: 'Florence',-    lastName: 'Nightingale'+    lastName: 'Nightingale',+    inventorOf: ['coxcomb chart', 'modern nursing']};// good - git diff with trailing commaconst hero = {     firstName: 'Florence',     lastName: 'Nightingale',+    inventorOf: ['coxcomb chart', 'modern nursing'],};

// badconst hero = {  firstName: 'Dana',  lastName: 'Scully'};const heroes = [  'Batman',  'Superman'];// goodconst hero = {  firstName: 'Dana',  lastName: 'Scully',};const heroes = [  'Batman',  'Superman',];// badfunction createHero(  firstName,  lastName,  inventorOf) {  // does nothing}// goodfunction createHero(  firstName,  lastName,  inventorOf,) {  // does nothing}// good (note that a comma must not appear after a "rest" element)function createHero(  firstName,  lastName,  inventorOf,  ...heroArgs) {  // does nothing}// badcreateHero(  firstName,  lastName,  inventorOf);// goodcreateHero(  firstName,  lastName,  inventorOf,);// good (note that a comma must not appear after a "rest" element)createHero(  firstName,  lastName,  inventorOf,  ...heroArgs);

// bad - raises exceptionconst luke = {}const leia = {}[luke, leia].forEach((jedi) => jedi.father = 'vader')// bad - raises exceptionconst reaction = "No! Thats impossible!"(async function meanwhileOnTheFalcon() {  // handle `leia`, `lando`, `chewie`, `r2`, `c3p0`  // ...}())// bad - returns `undefined` instead of the value on the next line - always happens when `return` is on a line by itself because of ASI!function foo() {  return    'search your feelings, you know it to be foo'}// goodconst luke = {};const leia = {};[luke, leia].forEach((jedi) => {  jedi.father = 'vader';});// goodconst reaction = "No! Thats impossible!";(async function meanwhileOnTheFalcon() {  // handle `leia`, `lando`, `chewie`, `r2`, `c3p0`  // ...}());// goodfunction foo() {  return 'search your feelings, you know it to be foo';}

// => this.reviewScore = 9;// badconst totalScore = new String(this.reviewScore); // typeof totalScore is "object" not "string"// badconst totalScore = this.reviewScore + ''; // invokes this.reviewScore.valueOf()// badconst totalScore = this.reviewScore.toString(); // isnt guaranteed to return a string// goodconst totalScore = String(this.reviewScore);

const inputValue = '4';// badconst val = new Number(inputValue);// badconst val = +inputValue;// badconst val = inputValue >> 0;// badconst val = parseInt(inputValue);// goodconst val = Number(inputValue);// goodconst val = parseInt(inputValue, 10);

// good/** * parseInt was the reason my code was slow. * Bitshifting the String to coerce it to a * Number made it a lot faster. */const val = inputValue >> 0;

2147483647 >> 0; // => 21474836472147483648 >> 0; // => -21474836482147483649 >> 0; // => -2147483647

const age = 0;// badconst hasAge = new Boolean(age);// goodconst hasAge = Boolean(age);// bestconst hasAge = !!age;