详解JavaScript中if语句优化和部分语法糖小技巧推荐

let name = \"zhangsan\";
if (name === \"zhangsan\") {
	console.log(\"zhangsan\"); // zhangsan
} else {
	console.log(\"lisi\");
}

if (name === \"zhangsan\") console.log(\"zhangsan\");
else console.log(\"lisi\");

let userInfo = {
	name: \"zhangsan\",
};
if (userInfo.name === \"zhangsan\") {
	console.log(\"zhangsan\");
}
if (!userInfo.age) {
	// userInfo.age--> false age属性不存在
	console.log(\"年龄属性不存在\");
}
userInfo.name === \"zhangsan\" && console.log(\"zhangsan\");
userInfo.age || console.log(\"年龄属性不存在\"); // 年龄属性不存在

let name = \"zhangsan\";
name === \"zhangsan\" ? console.log(\"zhangsan\") : console.log(\"lisi\");

let userObj = { name: \"zhangsan\", children: { name: \"lisi\" } };
if (userObj.children) {
  if (userObj.children.name == \"lisi\") {
    console.log(userObj.children.name);
  }
}
if (userObj.children && userObj.children.name == \"lisi\")
  console.log(userObj.children.name);

let age = \"22\";
if (age == \"22\" || age == \"24\" || age == \"25\") {
  console.log(age);
}
let ageArray = [\"22\", \"24\", \"25\"];
if (ageArray.includes(age)) {
  console.log(age);
}
if (ageArray.indexOf(age) > -1) {
  console.log(age);
}

let val = \"lisi\";
switch (val) {
  case \"zhangsan\":
    console.log(val);
    break;
  case \"lisi\":
    console.log(val);
    break;
  case \"xiaoming\":
    console.log(val);
    break;
  case \"xiaowang\":
    console.log(val);
    break;
  default:
    console.log(val);
}

let userArray = [
  { name: \"zhangsan\" },
  { name: \"lisi\" },
  { name: \"xiaoming\" },
  { name: \"xiaowang\" },
];

// 多重if else
if (userArray.name === \"zhangsan\") {
  console.log(userArray.name);
} else if (userArray.name === \"lisi\") {
  console.log(userArray.name);
} else if (userArray.name === \"xiaoming\") {
  console.log(userArray.name);
} else if (userArray.name === \"xiaowang\") {
  console.log(userArray.name);
} else {
  console.log(\"其他用户\");
}

function getUser(username) {
  return userArray.filter((item) => item.name == username)[0];
}
console.log(getUser(\"zhangsan\"));

let filterUser = function (username) {
  return `名字是${username}`;
};
let userMap = new Map([
  [\"zhangsan\", filterUser(\"zhangsan\")],
  [\"lisi\", filterUser(\"lisi\")],
  [\"xiaoming\", filterUser(\"xiaoming\")],
  [\"xiaowang\", filterUser(\"xiaowang\")],
]);
console.log(userMap.get(\"zhangsan\"));   // 名字是zhangsan

/**
 * 箭头函数
 *
 * */
function userInfo(name, age) {
  return `名字是:${name},年龄是:${age}`;
}
let userInfo = (name, age) => `名字是:${name},年龄是:${age}`;
console.log(userInfo(\"zhangsan\", \"23\"));

function log1() {
  console.log(1);
}
function log2() {
  console.log(2);
}
let num = 2;
if (num === 1) {
  log1();
} else {
  log2();
}
num === 1 ? log1() : log2();

let getUser = (name = \"zhangsan\", age = 23) =>
      `名字是:${name},年龄是:${age}`;

console.log(\"默认参数\", getUser());
console.log(\"传参\", getUser(\"lisi\", 29));

let num1 = +\"123\";
console.log(num1);

/**
 *
 * Null、Undefined 布尔值等特殊值处理,使用||结合!
 *
 * */
let name1 = undefined;
let name2 = null;
let name3 = true;
let name4 = false;
let name5 = \"lisi\";
console.log(name1 || \"其他人\"); // 其他人
console.log(name2 || \"其他人\"); // 其他人
console.log(name3 || \"其他人\"); // true
console.log(!name3 || \"其他人\"); // 其他人
console.log(name4 || \"其他人\"); // 其他人
console.log(name5 || \"其他人\"); // lisi
console.log(!name5 || \"其他人\"); // 其他人

let user = {
  name: \"zhangsan\",
  children: { name: \"lisi\", children: { name: \"xiaoming\" } },
};
let name1 = user?.name;
let name2 = user?.children?.name;
let name3 = user?.children?.children?.name;
console.log(name1);
console.log(name2);
console.log(name3);

const foo = null ?? \"default string\";
const test = undefined ?? \"default string\";
const test1 = 123 ?? \"default string\";
console.log(test); // \"default string\"
console.log(foo); // \"default string\"
console.log(test1); // 123
const baz = 0 ?? 42;
console.log(baz); // 0
const str = \"\" ?? 42;
const str1 = \"\" || 42;
console.log(str); // \"\"
console.log(str1); // 42