在JS中避免过多的使用IF语句方法有哪些

本篇内容主要讲解"在JS中避免过多的使用IF语句方法有哪些"，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习"在JS中避免过多的使用IF语句方法有哪些"吧!

1. 三元运算符

(1) 事例1

带有IF的代码：

function saveCustomer(customer) {   if (isCustomerValid(customer)) {     database.save(customer)   } else {     alert('customer is invalid')   } }

重构后代码：

function saveCustomer(customer) {   return isCustomerValid(customer)     ? database.save(customer)     : alert('customer is invalid') }

使用 ES6

const saveCustomer = customer =>    isCustomerValid(customer)?      database.save(customer) : alert('customer is invalid')

(2) 事例2

带有IF的代码：

 function customerValidation(customer) {    if (!customer.email) {      return error('email is require')    } else if (!customer.login) {     return error('login is required')    } else if (!customer.name) {      return error('name is required')    } else {      return customer   } }

重构后代码：

const customercustomerValidation = customer =>   !customer.email   ? error('email is required')   : !customer.login ? error('login is required')   : !customer.name  ? error('name is required')                     : customer

(3) 事例3

带有IF的代码：

 function getEventTarget(evt) {      if (!evt) {          evt = window.event;      }      if (!evt) {          return;      }      const target;      if (evt.target) {         target = evt.target;     } else {         target = evt.srcElement;     }     return target; }

重构后代码：

function getEventTarget(evt) {   evtevt = evt || window.event;   return evt && (evt.target || evt.srcElement); }

2. 短路运算符

(1) 事例1

带有IF的代码：

 const isOnline = true;  const makeReservation= ()=>{};  const user = {      name:'Damian',      age:32,      dni:33295000  };    if (isOnline){     makeReservation(user); }

重构后代码：

const isOnline = true; const makeReservation= ()=>{}; const user = {     name:'Damian',     age:32,     dni:33295000 };  isOnline&&makeReservation(user);

(2) 事例2

带有IF的代码：

 const active = true;  const loan = {      uuid:123456,      ammount:10,      requestedBy:'rick'  };    const sendMoney = ()=>{};   if (active&&loan){     sendMoney(); }

重构后代码：

const active = true; const loan = {     uuid:123456,     ammount:10,     requestedBy:'rick' };  const sendMoney = ()=>{};  ctive && loan && sendMoney();

3. 函数委托

事例1

带有IF的代码：

function itemDropped(item, location) {     if (!item) {         return false;     } else if (outOfBounds(location) {         var error = outOfBounds;         server.notify(item, error);         items.resetAll();         return false;     } else {        animateCanvas();        server.notify(item, location);        return true;    }

重构后代码：

 function itemDropped(item, location) {      const dropOut = function() {          server.notify(item, outOfBounds);         items.resetAll();          return false;      }       const dropIn = function() {          server.notify(item, location);         animateCanvas();         return true;     }      return !!item && (outOfBounds(location) ? dropOut() : dropIn()); }

4. 非分支策略

此技巧尝试避免使用switch语句，相反是用键/值创建一个映射并使用一个函数访问作为参数传递的键的值。

(1) 事例1

带有switch的代码：

 switch(breed){      case 'border':        return 'Border Collies are good boys and girls.';        break;        case 'pitbull':        return 'Pit Bulls are good boys and girls.';        break;        case 'german':        return 'German Shepherds are good boys and girls.';       break;     default:       return 'Im default' }

重构后代码：

const dogSwitch = (breed) =>({   "border": "Border Collies are good boys and girls.",   "pitbull": "Pit Bulls are good boys and girls.",   "german": "German Shepherds are good boys and girls.",   })[breed]||'Im the default';   dogSwitch("border xxx")

5. 作为数据的函数

我们知道在JS中函数是第一个类，所以使用它我们可以把代码分割成一个函数对象。

带有IF的代码：

 const calc = {      run: function(op, n1, n2) {          const result;          if (op == "add") {              result = n1 + n2;          } else if (op == "sub" ) {              result = n1 - n2;          } else if (op == "mult" ) {              result = n1 * n2;         } else if (op == "div" ) {             result = n1 / n2;         }         return result;     } }  calc.run("sub", 5, 3); //2

重构后代码：

 const calc = {      add : function(a,b) {          return a + b;      },      sub : function(a,b) {          return a - b;      },      mult : function(a,b) {          return a * b;     },     div : function(a,b) {         return a / b;     },     run: function(fn, a, b) {         return fn && fn(a,b);     } }  calc.run(calc.mult, 7, 4); //28

6. 多态性

多态性是对象具有多种形式的能力。OOP中多态性最常见的用法是使用父类引用来引用子类对象。

带有IF的代码：

 const bob = {    name:'Bob',    salary:1000,    job_type:'DEVELOPER'  };    const mary = {    name:'Mary',    salary:1000,   job_type:'QA' };  const calc = (person) =>{      if (people.job_type==='DEVELOPER')         return person.salary+9000*0.10;      if (people.job_type==='QA')         return person.salary+1000*0.60; }  console.log('Salary',calc(bob)); console.log('Salary',calc(mary));

重构后代码：

 const qaSalary  = (base) => base+9000*0.10;  const devSalary = (base) => base+1000*0.60;    //Add function to the object.  const bob = {    name:'Bob',    salary:1000,    job_type:'DEVELOPER',    calc: devSalary };  const mary = {   name:'Mary',   salary:1000,   job_type:'QA',   calc: qaSalary };  console.log('Salary',bob.calc(bob.salary)); console.log('Salary',mary.calc(mary.salary));

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