在JS中避免过多的使用IF语句方法有哪些
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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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文章起源:http://scyanting.com/article/iehhgh.html