本文罗列JavaScript代码中常见的代码坏味道,如双向数据绑定临时定时器,双向数据绑定的坑,复杂的分支语句,重复赋值等,对它们进行分析如现场还原,糟糕代码回顾,问题诊断和识别(通过ESlint或其他工具),代码重构方案,给出了怎么写好代码的一手经验~
绕来绕去,很烧脑
问题现场:
如果单词以辅音开头(或辅音集),把它剩余的步伐移到前面,并且添加上『ay』如pig -> igpay
如果单词以元音开头,保持顺序但是在结尾加上『way』如,egg->eggway等
糟糕代码:
/* const */ var CONSONANTS = 'bcdfghjklmnpqrstvwxyz';
/* const */ var VOWELS = 'aeiou';
function englishToPigLatin(english) {
/* const */ var SYLLABLE = 'ay';
var pigLatin = '';
if (english !== null && english.length > 0 &&
(VOWELS.indexOf(english[0]) > -1 ||
CONSONANTS.indexOf(english[0]) > -1 )) {
if (VOWELS.indexOf(english[0]) > -1) {
pigLatin = english + SYLLABLE;
} else {
var preConsonants = '';
for (var i = 0; i < english.length; ++i) {
if (CONSONANTS.indexOf(english[i]) > -1) {
preConsonants += english[i];
if (preConsonants == 'q' &&
i+1 < english.length && english[i+1] == 'u') {
preConsonants += 'u';
i += 2;
break;
}
} else { break; }
}
pigLatin = english.substring(i) + preConsonants + SYLLABLE;
}
}
return pigLatin;
}
问题在哪:
检测出问题:
关于Lint的配置项:如最大语句数,复杂度,最大嵌套数,最大长度,最多传参,最多嵌套回调
/*jshint maxstatements:15, maxdepth:2, maxcomplexity:5 */
/*eslint max-statements:[2, 15], max-depth:[1, 2], complexity:[2, 5] */
7:0 - Function 'englishToPigLatin' has a complexity of 7.
7:0 - This function has too many statements (16). Maximum allowed is 15.
22:10 - Blocks are nested too deeply (5).
测试先行:
describe('Pig Latin', function() {
describe('Invalid', function() {
it('should return blank if passed null', function() {
expect(englishToPigLatin(null)).toBe('');
});
it('should return blank if passed blank', function() {
expect(englishToPigLatin('')).toBe('');
});
it('should return blank if passed number', function() {
expect(englishToPigLatin('1234567890')).toBe('');
});
it('should return blank if passed symbol', function() {
expect(englishToPigLatin('~!@#$%^&*()_+')).toBe('');
});
});
describe('Consonants', function() {
it('should return eastbay from beast', function() {
expect(englishToPigLatin('beast')).toBe('eastbay');
});
it('should return estionquay from question', function() {
expect(englishToPigLatin('question')).toBe('estionquay');
});
it('should return eethray from three', function() {
expect(englishToPigLatin('three')).toBe('eethray');
});
});
describe('Vowels', function() {
it('should return appleay from apple', function() {
expect(englishToPigLatin('apple')).toBe('appleay');
});
});
});
重构后代码:
const CONSONANTS = ['th', 'qu', 'b', 'c', 'd', 'f', 'g', 'h', 'j', 'k',
'l', 'm', 'n', 'p', 'q', 'r', 's', 't', 'v', 'w', 'x', 'y', 'z'];
const VOWELS = ['a', 'e', 'i', 'o', 'u'];
const ENDING = 'ay';
let isValid = word => startsWithVowel(word) || startsWithConsonant(word);
let startsWithVowel = word => !!~VOWELS.indexOf(word[0]);
let startsWithConsonant = word => !!~CONSONANTS.indexOf(word[0]);
let getConsonants = word => CONSONANTS.reduce((memo, char) => {
if (word.startsWith(char)) {
memo += char;
word = word.substr(char.length);
}
return memo;
}, '');
function englishToPigLatin(english='') {
if (isValid(english)) {
if (startsWithVowel(english)) {
english += ENDING;
} else {
let letters = getConsonants(english);
english = `${english.substr(letters.length)}${letters}${ENDING}`;
}
}
return english;
}
数据对比:
max-statements: 16 → 6
max-depth: 5 → 2
complexity: 7 → 3
max-len: 65 → 73
max-params: 1 → 2
max-nested-callbacks: 0 → 1
相关资源:
jshint - jshint.com/
eslint - eslint.org/
jscomplexity - jscomplexity.org/
escomplex - github.com/philbooth/e…
jasmine - jasmine.github.io/
粘贴复制
问题现场:
糟糕的代码:
var boxes = document.querySelectorAll('.Box');
[].forEach.call(boxes, function(element, index) {
element.innerText = "Box: " + index;
element.style.backgroundColor =
'#' + (Math.random() * 0xFFFFFF << 0).toString(16);
});
var circles = document.querySelectorAll(".Circle");
[].forEach.call(circles, function(element, index) {
element.innerText = "Circle: " + index;
element.style.color =
'#' + (Math.random() * 0xFFFFFF << 0).toString(16);
});
问题出在哪:
因为我们在粘贴复制!!
检测出问题:
检查出粘贴复制和结构类似的代码片段 - jsinspect
github.com/danielstjul…
从你的JS,TypeScript,C#,Ruby,CSS,HTML等源代码中找到粘贴复制的部分 - JSCPD
github.com/kucherenko/…
重构后代码:
- Let's pull out the random color portion...
- Let's pull out the weird [].forEach.call portion...
- Let's try to go further...
let randomColor = () => `#${(Math.random() * 0xFFFFFF << 0).toString(16)};
let $ = selector => [].slice.call(document.querySelectorAll(selector || '*'));
let updateElement = (selector, textPrefix, styleProperty) => {
$(selector).forEach((element, index) => {
element.innerText = textPrefix + ': ' + index;
element.style[styleProperty] = randomColor();
});
}
updateElement('.Box', 'Box', 'backgroundColor'); // 12: Refactored
updateElement('.Circle', 'Circle', 'color'); // 14: Refactored
复杂的分支语句
糟糕的代码:
function getArea(shape, options) {
var area = 0;
switch (shape) {
case 'Triangle':
area = .5 * options.width * options.height;
break;
case 'Square':
area = Math.pow(options.width, 2);
break;
case 'Rectangle':
area = options.width * options.height;
break;
default:
throw new Error('Invalid shape: ' + shape);
}
return area;
}
getArea('Triangle', { width: 100, height: 100 });
getArea('Square', { width: 100 });
getArea('Rectangle', { width: 100, height: 100 });
getArea('Bogus');
问题出在哪:
违反了 open/close 原则:
软件元素(类,模块和方法等)应该易于被打开扩展,但是除了本身不要多于的修改。既代码本身可以允许它的行为被扩展,但是不要修改源代码
可以使用诸如检查:
no-switch - disallow the use of the switch statement
no-complex-switch-case - disallow use of complex switch statements
重构后代码:
这时候添加一个代码就不像之前那样该原先的switch,直到它又长又臭,还容易把之前的代码逻辑broken掉。
(function(shapes) { // triangle.js
var Triangle = shapes.Triangle = function(options) {
this.width = options.width;
this.height = options.height;
};
Triangle.prototype.getArea = function() {
return 0.5 * this.width * this.height;
};
}(window.shapes = window.shapes || {}));
function getArea(shape, options) {
var Shape = window.shapes[shape], area = 0;
if (Shape && typeof Shape === 'function') {
area = new Shape(options).getArea();
} else {
throw new Error('Invalid shape: ' + shape);
}
return area;
}
getArea('Triangle', { width: 100, height: 100 });
getArea('Square', { width: 100 });
getArea('Rectangle', { width: 100, height: 100 });
getArea('Bogus');
// circle.js
(function(shapes) {
var Circle = shapes.Circle = function(options) {
this.radius = options.radius;
};
Circle.prototype.getArea = function() {
return Math.PI * Math.pow(this.radius, 2);
};
Circle.prototype.getCircumference = function() {
return 2 * Math.PI * this.radius;
};
}(window.shapes = window.shapes || {}));
魔法数字/字符串的坏味道
糟糕代码:
如上面看到的,如Magic Strings,对于诸如Triangle,Square这些就是特殊字符串。
问题出在哪:
这些魔法数字和字符串是直接写死在代码中,不容易修改和阅读。注入password.length > 9,这里面的9是指 MAX_PASSWORD_SIZE ,这样先定义后使用更清晰。同时如果多个地方需要这个判断规则,也可以避免多次修改类似9这样的数字
en.wikipedia.org/wiki/Magic_…
stackoverflow.com/questions/4…
重构后代码:
1 通过对象
var shapeType = {
triangle: 'Triangle' // 2: Object Type
};
function getArea(shape, options) {
var area = 0;
switch (shape) {
case shapeType.triangle: // 8: Object Type
area = .5 * options.width * options.height;
break;
}
return area;
}
getArea(shapeType.triangle, { width: 100, height: 100 }); // 15:
2 通过 const 和 symbols
const shapeType = {
triangle: Symbol() // 2: Enum-ish
};
function getArea(shape, options) {
var area = 0;
switch (shape) {
case shapeType.triangle: // 8: Enum-ish
代码深渊
糟糕代码:
Person.prototype.brush = function() {
var that = this;
this.teeth.forEach(function(tooth) {
that.clean(tooth);
});
console.log('brushed');
};
问题出在哪:
奇奇怪怪的 self /that/_this 等
使用一下的eslint:
- no-this-assign (eslint-plugin-smells)
- consistent-this
- no-extra-bind
重构后代码:
利用Function.bind, 2nd parameter of forEach, es6
Person.prototype.brush = function() {
this.teeth.forEach(function(tooth) {
this.clean(tooth);
}.bind(this)); // 4: Use .bind() to change context
console.log('brushed');
};
Person.prototype.brush = function() {
this.teeth.forEach(function(tooth) {
this.clean(tooth);
}, this); // 4: Use 2nd parameter of .forEach to change context
console.log('brushed');
};
Person.prototype.brush = function() {
this.teeth.forEach(tooth => { // 2: Use ES6 Arrow Function to bind `this`
this.clean(tooth);
});
console.log('brushed');
};
脆裂的字符拼接
糟糕代码:
var build = function(id, href, text) {
return $( " + href + "' id='" + id + "'>" +
text + "" );
}
问题出在哪:
代码很丑陋,也很啰嗦,不直观。
使用 ES6的模板字符串(字符串插值和多行)
很多工具和框架也都提供了响应的支持,如lodash/underscore,angular,react 等
重构后代码:
jQuery询问
糟糕代码:
$(document).ready(function() {
$('.Component')
.find('button')
.addClass('Component-button--action')
.click(function() { alert('HEY!'); })
.end()
.mouseenter(function() { $(this).addClass('Component--over'); })
.mouseleave(function() { $(this).removeClass('Component--over'); })
.addClass('initialized');
});
问题出在哪:
太多的链式调用
重构后代码:
// Event Delegation before DOM Ready
$(document).on('mouseenter mouseleave', '.Component', function(e) {
$(this).toggleClass('Component--over', e.type === 'mouseenter');
});
$(document).on('click', '.Component button', function(e) {
alert('HEY!');
});
$(document).ready(function() {
$('.Component button').addClass('Component-button--action');
});
临时定时器
糟糕代码:
setInterval(function() {
console.log('start setInterval');
someLongProcess(getRandomInt(2000, 4000));
}, 3000);
function someLongProcess(duration) {
setTimeout(
function() { console.log('long process: ' + duration); },
duration
);
}
function getRandomInt(min, max) {
return Math.floor(Math.random() * (max - min + 1)) + min;
}
问题出在哪:
out of sync timer 不能确认时序和执行
重构后代码:
等 3s 去执行timer(setTimeout),然后调用 someLongProcess (long process: random time ),接着在循环
使用setInterval fn(其中在进行 long process),还是通过callback传递来反复setTimeout(timer, )
setTimeout(function timer() {
console.log('start setTimeout')
someLongProcess(getRandomInt(2000, 4000), function() {
setTimeout(timer, 3000);
});
}, 3000);
function someLongProcess(duration, callback) {
setTimeout(function() {
console.log('long process: ' + duration);
callback();
}, duration);
}
/* getRandomInt(min, max) {} */
重复赋值
糟糕代码:
data = this.appendAnalyticsData(data);
data = this.appendSubmissionData(data);
data = this.appendAdditionalInputs(data);
data = this.pruneObject(data);
问题出在哪:
有些重复和啰嗦
eslint-plugin-smells
重构后代码:
1 嵌套的函数调用
2 forEach
3 reduce
4 flow
// 1
data = this.pruneObject(
this.appendAdditionalInputs(
this.appendSubmissionData(
this.appendAnalyticsData(data)
)
)
);
// 2
var funcs = [
this.appendAnalyticsData,
this.appendSubmissionData,
this.appendAdditionalInputs,
this.pruneObject
];
funcs.forEach(function(func) {
data = func(data);
});
// 3
// funcs 定义如上
data = funcs.reduce(function(memo, func) {
return func(memo);
}, data);
// 4
data = _.flow(
this.appendAnalyticsData,
this.appendSubmissionData,
this.appendAdditionalInputs,
this.pruneObject
)(data);
不合理的情报
糟糕代码:
function ShoppingCart() { this.items = []; }
ShoppingCart.prototype.addItem = function(item) {
this.items.push(item);
};
function Product(name) { this.name = name; }
Product.prototype.addToCart = function() {
shoppingCart.addItem(this);
};
var shoppingCart = new ShoppingCart();
var product = new Product('Socks');
product.addToCart();
console.log(shoppingCart.items);
问题出在哪:
依赖被紧紧的耦合了
相互调用,耦合!如 product 和 shoppingCart 关系
重构后代码:
1 dependency injection 依赖注入
2 消息经纪人broker
function Product(name, shoppingCart) { // 6: Accept Dependency
this.name = name;
this.shoppingCart = shoppingCart; // 8: Save off Dependency
}
Product.prototype.addToCart = function() {
this.shoppingCart.addItem(this);
};
var shoppingCart = new ShoppingCart();
var product = new Product('Socks', shoppingCart); // 15: Pass in Dependency
product.addToCart();
console.log(shoppingCart.items);
var channel = postal.channel(); // 1: Broker
function ShoppingCart() {
this.items = [];
channel.subscribe('shoppingcart.add', this.addItem); // 5: Listen to Message
}
ShoppingCart.prototype.addItem = function(item) {
this.items.push(item);
};
function Product(name) { this.name = name; }
Product.prototype.addToCart = function() {
channel.publish('shoppingcart.add', this); // 13: Publish Message
};
var shoppingCart = new ShoppingCart();
var product = new Product('Socks');
product.addToCart();
console.log(shoppingCart.items);
不断的交互调用
糟糕代码:
var search = document.querySelector('.Autocomplete');
search.addEventListener('input', function(e) {
// Make Ajax call for autocomplete
console.log(e.target.value);
});
问题出在哪:
会造成卡顿,多余的计算等
重构后代码:
throttle 和 debounce
var search = document.querySelector('.Autocomplete');
search.addEventListener('input', _.throttle(function(e) {
// Make Ajax call for autocomplete
console.log(e.target.value);
}, 500));
var search = document.querySelector('.Autocomplete');
search.addEventListener('input', _.debounce(function(e) {
// Make Ajax call for autocomplete
console.log(e.target.value);
}, 500));
匿名算法
糟糕代码:
var search = document.querySelector('.Autocomplete');
search.addEventListener('input', _.debounce(function(e) {
// Make Ajax call for autocomplete
console.log(e.target.value);
}, 500));
问题出在哪:
匿名函数是个好东西,但是给函数命名可以帮助我们:
- Stack Trace(结合Devtools,跟容易debug)
- Dereferencing
- Code Reuse
重构后代码:
var search = document.querySelector('.Autocomplete');
search.addEventListener('input', _.debounce(function matches(e) {
console.log(e.target.value);
}, 500));
未明确的执行
糟糕代码:
明确触发时机而不是,写在 domready
$(document).ready(function() {
// wire up event handlers
// declare all the things
// etc...
});
问题出在哪:
很难做单元测试
重构后代码:
利用单例模块,加上构建器函数
单例模式(单例有个init 方法,来Kick off) & 构造函数(new Application() -> 在原来的构造函数中Kick off your code!)
(function(myApp) {
myApp.init = function() {
// kick off your code
};
myApp.handleClick = function() {}; // etc...
}(window.myApp = window.myApp || {}));
// Only include at end of main application...
$(document).ready(function() {
window.myApp.init();
});
var Application = (function() {
function Application() {
// kick off your code
}
Application.prototype.handleClick = function() {};
return Application;
}());
// Only include at end of main application...
$(document).ready(function() {
new Application();
});
双向数据绑定
糟糕代码:
随便看看你们手头的MVVM项目(如Angular的等)
问题出在哪:
很难定位执行顺序和数据流(Hard to track execution & data flow )
(也是Angular1.x被大力吐槽的地方,被React的Flux)
重构后代码:
方案: flux(action, dispatcher, store->view)
React Flux
An Angular2 Todo App: First look at App Development in Angular2
结语
更多的lint规则,在npm上搜索 eslint-plugin 查找