深入淺出代碼優化﹣if/else

if (workIsDone === true) {
  eatDinner();
} else {
  keepCoding();
}

'' 或 "" 或 ``
0 或 -0
null
undefined
NaN
false

!(A || B) === (!A && !B); // true
!(A && B) === (!A || !B); // true

const enableGA = !(isAuthor() || isTestingEnvironment());
const betterEnableGA = !isAuthor() && !isTestingEnvironment();

const enableGA = isNotAuthor() && isNotTestingEnvironment();

if (user && user.canDeletePost) {
  deletePost();
}

user && user.canDeletePost && deletePost();

const userCanDeletePost = user && user.canDeletePost;
userCanDeletePost && deletePost();

let strength = null;

if (password.length > 7) {
  strength = "Strong";
} else {
  strength = "Weak";
}

const strength = (password.length > 7 && "Strong") || "Weak";

(condition && A) || B;

// 例如：
let password = "abcdefg1234";
(password.length > 7 && false) || "Weak"; // 'Weak'

password = "a";
(password.length > 7 && false) || "Weak"; // 'Weak'

condition ? A : B;

const strength = password.length > 7 ? "Strong" : "Weak";

let xmlhttp = null;

if (window.XMLHttpRequest) {
  // 現代瀏覽器
  xmlhttp = new XMLHttpRequest();
} else if (window.ActiveXObject) {
  // 舊 IE 版本 (IE <= 6)
  xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
}

const xmlhttp =
  (window.XMLHttpRequest && new XMLHttpRequest()) ||
  (window.ActiveXObject && new ActiveXObject("Microsoft.XMLHTTP")) ||
  null;

const xmlhttp = window.XMLHttpRequest
  ? new XMLHttpRequest()
  : window.ActiveXObject
  ? new ActiveXObject("Microsoft.XMLHTTP")
  : null;

// 這個判斷式
A
  ? B
  : C
  ? D
  : E
  ? F
  : G(
      // 等同以下判斷式
      A ? B : C ? D : E ? F : G
    ); // B

((A ? B : C) ? D : E) ? F : G; // F

workIsDone ? eatDinner() : keepCoding();