JS 中的 IF 语句优化技巧
Sonder
2020-08-04
5467字
14分钟
浏览 (2.3k)
Damian Cipolat
原文：https://dev.to/damxipo/avoid-use-if-on-our-js-scripts-1b95
1. 三元运算符
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')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 customerValidation = customer =>
!customer.email ? error('email is required')
: !customer.login ? error('login is required')
: !customer.name ? error('name is required')
: customer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) {
evt = evt || window.event;
return evt && (evt.target || evt.srcElement);
}2.短路运算符
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);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 = ()=>{};
active && 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。
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); //286.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));