去除 JavaScript 代码的怪味
原文：《 ELIMINATE JAVASCRIPT CODE SMELLS 》
作者： @elijahmanor
笔记：涂鸦码农
难闻的代码
/* 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; }
为毛是这个味？
很多原因：
- 声明过多
- 嵌套太深
- 复杂度太高
检查工具
Lint 规则
/*jshint maxstatements:15, maxdepth:2, maxcomplexity:5 */ /*jshint 最多声明:15, 最大深度:2, 最高复杂度:5*/ /*eslint max-statements:[2, 15], max-depth:[1, 2], complexity:[2, 5] */
结果
7:0 - Function 'englishToPigLatin' has a complexity of 7. //englishToPigLatin 方法复杂度为 7 7:0 - This function has too many statements (16). Maximum allowed is 15. // 次方法有太多声明(16)。最大允许值为 15。 22:10 - Blocks are nested too deeply (5). // 嵌套太深(5)
重构
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}${ENDING}`; } } return english; } 重构后统计
- max-statements（最多声明）: 16 → 6
- max-depth（最大嵌套）: 5 → 2
- complexity（复杂度）: 7 → 3
- max-len（最多行数）: 65 → 73
- max-params（最多参数）: 1 → 2
- max-nested-callbacks（最多嵌套回调）: 0 → 1
资源
jshint -http://jshint.com/
eslint - http://eslint.org/
jscomplexity - http://jscomplexity.org/
escomplex - https://github.com/philbooth/escomplex
jasmine - http://jasmine.github.io/
复制粘贴代码的味道
已有功能…
已有代码，BOX.js
// ... more code ... var boxes = document.querySelectorAll('.Box'); [].forEach.call(boxes, function(element, index) { element.innerText = "Box: " + index; element.style.backgroundColor = '#' + (Math.random() * 0xFFFFFF << 0).toString(16); }); // ... more code ...
那么，现在想要这个功能
于是，Duang! CIRCLE.JS 就出现了…
// ... more code ... var circles = document.querySelectorAll(".Circle"); [].forEach.call(circles, function(element, index) { element.innerText = "Circle: " + index; element.style.color = '#' + (Math.random() * 0xFFFFFF << 0).toString(16); }); // ... more code ...
为毛是这个味？因为我们复制粘贴了！
工具
JSINSPECT
检查复制粘贴和结构相似的代码
一行命令：
jsinspect
JSCPD
程序源码的复制 / 粘贴检查器
(JavaScript, TypeScript, C#, Ruby, CSS, SCSS, HTML, 等等都适用…)
jscpd -f **/*.js -l 1 -t 30 --languages javascript
怎么能不被发现？重构
把随机颜色部分丢出去…
let randomColor = () => `#${(Math.random() * 0xFFFFFF << 0).toString(16)}; let boxes = document.querySelectorAll(".Box"); [].forEach.call(boxes, (element, index) => { element.innerText = "Box: " + index; element.style.backgroundColor = randomColor(); }); let circles = document.querySelectorAll(".Circle"); [].forEach.call(circles, (element, index) => { element.innerText = "Circle: " + index; element.style.color = randomColor(); });
再重构
再把怪异的 [].forEach.call 部分丢出去…
let randomColor = () => `#${(Math.random() * 0xFFFFFF << 0).toString(16)}; let $$ = selector => [].slice.call(document.querySelectorAll(selector || '*')); $$('.Box').forEach((element, index) => { element.innerText = "Box: " + index; element.style.backgroundColor = randomColor(); }); $$(".Circle").forEach((element, index) => { element.innerText = "Circle: " + index; element.style.color = randomColor(); });
再再重构
let randomColor = () => `#${(Math.random() * 0xFFFFFF << 0).toString(16)}; let $$ = 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'); updateElement('.Circle', 'Circle', 'color');
资源
- jsinspect
- jscpd
- CodePen
switch 味道
难闻的代码
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');
为毛是这个味？违背“ 打开 / 关闭原则 ”
增加个新形状
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; case 'Circle': area = Math.PI * Math.pow(options.radius, 2); break; default: throw new Error('Invalid shape: ' + shape); } return area; }
加点设计模式
(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');
再增加新形状时
// 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 || {}));
还有其它的味道吗？神奇的字符串
function getArea(shape, options) { var area = 0; switch (shape) { case 'Triangle': area = .5 * options.width * options.height; break; /* ... more code ... */ } return area; } getArea('Triangle', { width: 100, height: 100 });
神奇的字符串重构为对象类型
var shapeType = { triangle: 'Triangle' }; function getArea(shape, options) { var area = 0; switch (shape) { case shapeType.triangle: area = .5 * options.width * options.height; break; } return area; } getArea(shapeType.triangle, { width: 100, height: 100 });
神奇字符重构为 CONST & SYMBOLS
const shapeType = { triangle: new Symbol() }; function getArea(shape, options) { var area = 0; switch (shape) { case shapeType.triangle: area = .5 * options.width * options.height; break; } return area; } getArea(shapeType.triangle, { width: 100, height: 100 });
工具！？！
木有 :(
ESLINT-PLUGIN-SMELLS
用于 JavaScript Smells（味道） 的 ESLint 规则
规则
- no-switch - 不允许使用 switch 声明
- no-complex-switch-case - 不允许使用复杂的 switch 声明
资源
- CodePen
- Addy Osmani’s JavaScript Design Patterns eBook
- ESLint
- eslint-plugin-smells
- ES6 Scoping
- ES6 Symbols
- Learn ES6
this 深渊的味道
难闻的代码
function Person() { this.teeth = [{ clean: false }, { clean: false }, { clean: false }]; }; Person.prototype.brush = function() { var that = this; this.teeth.forEach(function(tooth) { that.clean(tooth); }); console.log('brushed'); }; Person.prototype.clean = function(tooth) { tooth.clean = true; } var person = new Person(); person.brush(); console.log(person.teeth);
为什么是这个味？that 还是 self 还是 selfie
替换方案1) bind
Person.prototype.brush = function() { this.teeth.forEach(function(tooth) { this.clean(tooth); }.bind(this)); console.log('brushed'); };
替换方案2) forEach 的第二个参数
Person.prototype.brush = function() { this.teeth.forEach(function(tooth) { this.clean(tooth); }, this); console.log('brushed'); };
替换方案3) ECMAScript 2015 (ES6)
Person.prototype.brush = function() { this.teeth.forEach(tooth => { this.clean(tooth); }); console.log('brushed'); };
4a) 函数式编程
Person.prototype.brush = function() { this.teeth.forEach(this.clean); console.log('brushed'); };
4b) 函数式编程
Person.prototype.brush = function() { this.teeth.forEach(this.clean.bind(this)); console.log('brushed'); };
工具
ESLint
- no-this-assign (eslint-plugin-smells)
- consistent-this
- no-extra-bind
字符串连接的味道
难闻的代码
var build = function(id, href) { return $( "<div id='tab'><a href='" + href + "' id='"+ id + "'></div>" ); }
为毛是这个味？因为字符串连接
替换方案
@thomasfuchs 推文上的 JavaScript 模板引擎
function t(s, d) { for (var p in d) s = s.replace(new RegExp('{' + p + '}', 'g'), d[p]); return s; } var build = function(id, href) { var options = { id: id href: href }; return t('<div id="tab"><a href="{href}" id="{id}"></div>', options); }
替换方案2) ECMAScript 2015 (ES6) 模板字符串
var build = (id, href) => `<div id="tab"><a href="${href}" id="${id}"></div>`;
替换方案3) ECMAScript 2015 (ES6) 模板字符串 (多行)
替换方案4) 其它小型库或大型库 / 框架
- Lowdash 或 Underscore
- Angular
- React
- Ember
- 等等…
工具
ESLINT-PLUGIN-SMELLS
no-complex-string-concat资源
Tweet Sized JavaScript Templating Engine by @thomasfuchs
Learn ECMAScript 2015 (ES6) - http://babeljs.io/docs/learn-es6/
jQuery 调查
难闻的代码
$(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'); });
为毛是这个味？丧心病狂的链式调用
愉快地重构吧
// Event Delegation before DOM Ready $(document).on('mouseenter mouseleave', '.Component', function(e) { $(this).toggleClass('Component--over', e.type === 'mouseenter'); }); $(document).on('click', '.Component', function(e) { alert('HEY!'); }); $(document).ready(function() { $('.Component button').addClass('Component-button--action'); });
最终 Demo
See the Pen pvQQZw by Elijah Manor ( @elijahmanor ) on CodePen .
正文到此结束
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