11个Javascript小技巧帮你提升代码质量(小结)

// 逻辑都写在一起，需要将所有逻辑看完才知道这段代码是干嘛的，局部逻辑无法复用
function main() {
 $.ajax.get('/getData').then((res) => {
  const ul = document.getElementById('ul');
  ul.innerHTML = res.list.map(text => `<li class="li">${text}</li>`).join('\n');
  const list = document.getElementsByClassName('li');
  for (let i = 0; i < list.length; i ++) {
   list[i].addEventListener('focus', () => {
    // do something
   });
  }
 });
}

function getData() {
 return $.ajax.get('/getData').then((res) => res.data.list);
}
function showList(list) {
 const ul = document.getElementById('ul');
 ul.innerHTML = list.map(text => `<li class="li">${text}</li>`).join('\n');
}
function addEvent() {
 const list = document.getElementsByClassName('li');
 for (let i = 0; i < list.length; i ++) {
  list[i].addEventListener('focus', () => {
   // do something
  });
 }
}
// 逻辑清晰，一眼读懂每一步在做什么，某些提炼出来的函数还可以被复用
async function main() {
 const list = await getData(); // 获取数据
 showList(list); // 显示页面
 addEvent(); // 添加事件
}

// 合并前
function main( currPage ){
 if ( currPage <= 0 ){
  currPage = 0;
  jump( currPage ); // 跳转
 }else if ( currPage >= totalPage ){
  currPage = totalPage;
  jump( currPage ); // 跳转
 }else{
  jump( currPage ); // 跳转
 }
};

// 合并后
function main( currPage ){
 if ( currPage <= 0 ){
  currPage = 0;
 }else if ( currPage >= totalPage ){
  currPage = totalPage;
 }
 jump( currPage ); // 把jump 函数独立出来
};

// 根据不同季节决定打折力度
function getPrice( price ){
 var date = new Date();
 if ( date.getMonth() >= 6 && date.getMonth() <= 9 ){ // 夏天
  return price * 0.8;
 }
 return price;
};


// 是否是夏天
function isSummer(){
 var date = new Date();
 return date.getMonth() >= 6 && date.getMonth() <= 9;
};
// 提炼条件后
function getPrice( price ){
 if ( isSummer() ){
  return price * 0.8;
 }
 return price;
};

// 判断是什么浏览器
function getBrowser(){
 const str = navigator.userAgent;
 if (str.includes('QQBrowser')) {
 return 'qq';
 } else if (str.includes('Chrome')) {
 return 'chrome';
 } else if (str.includes('Safari')) {
  return 'safri';
 } else if (str.includes('Firefox')) {
  return 'firefox';
 } else if(explorer.indexOf('Opera') >= 0){
  return 'opera';
 } else if (str.includes('msie')) {
  return 'ie';
 } else {
  return 'other';
 }
};


// 循环判断，将对应关系抽象为配置，更加清晰明确
function getBrowser(){
 const str = navigator.userAgent;
 const list = [
  {key: 'QQBrowser', browser: 'qq'},
  {key: 'Chrome', browser: 'chrome'},
  {key: 'Safari', browser: 'safari'},
  {key: 'Firefox', browser: 'firefox'},
  {key: 'Opera', browser: 'opera'},
  {key: 'msie', browser: 'ie'},
 ];
 for (let i = 0; i < list.length; i++) {
  const item = list[i];
  if (str.includes(item.key)) {return item.browser};
 }
 return 'other';
}

function del( obj ){
 var ret;
 if ( !obj.isReadOnly ){ // 不为只读的才能被删除
  if ( obj.isFolder ){ // 如果是文件夹
   ret = deleteFolder( obj );
  }else if ( obj.isFile ){ // 如果是文件
   ret = deleteFile( obj );
  }
 }
 return ret;
};

function del( obj ){
 if ( obj.isReadOnly ){ // 反转if 表达式
  return;
 }
 if ( obj.isFolder ){
  return deleteFolder( obj );
 }
 if ( obj.isFile ){
  return deleteFile( obj );
 }
};

function setUserInfo( id, name, address, sex, mobile, qq ){
 console.log( 'id= ' + id );
 console.log( 'name= ' +name );
 console.log( 'address= ' + address );
 console.log( 'sex= ' + sex );
 console.log( 'mobile= ' + mobile );
 console.log( 'qq= ' + qq );
};
setUserInfo( 1314, 'sven', 'shenzhen', 'male', '137********', 377876679 );

function setUserInfo( obj ){
 console.log( 'id= ' + obj.id );
 console.log( 'name= ' + obj.name );
 console.log( 'address= ' + obj.address );
 console.log( 'sex= ' + obj.sex );
 console.log( 'mobile= ' + obj.mobile );
 console.log( 'qq= ' + obj.qq );
};
setUserInfo({
 id: 1314,
 name: 'sven',
 address: 'shenzhen',
 sex: 'male',
 mobile: '137********',
 qq: 377876679
});

// 简单逻辑可以使用三目运算符
var global = typeof window !== "undefined" ? window : this;

// 复杂逻辑不适合使用
var ok = isString ? (isTooLang ? 2 : (isTooShort ? 1 : 0)) : -1;

var User = {
 id: null,
 name: null,
 setId: function( id ){
  this.id = id;
  return this;
 },
 setName: function( name ){
  this.name = name;
  return this;
 }
};
User
 .setId( 1314 )
 .setName( 'sven' );

var user = new User();
user.setId( 1314 );
user.setName( 'sven' );

var a = 1;
// 非纯函数
function sum(b) {
 return a + b;
}
// 非纯函数
function sum(b) {
 a = 2;
 return b;
}
// 非纯函数
function sum(b) {
 return b + Math.random();
}


// 纯函数
function sum (b, c) {
 return b + c;
}