去除 JavaScript 代碼的怪味

jopen 10年前發布 | 35K 次閱讀 JavaScript開發 JavaScript
難聞的代碼

/ 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;
}</pre> 
為毛是這個味？ 

很多原因： 


聲明過多 

嵌套太深 

復雜度太高 
</ul>
檢查工具 

Lint 規則 
/*jshint maxstatements:15, maxdepth:2, maxcomplexity:5 */
/*jshint 最多聲明:15, 最大深度:2, 最高復雜度:5*/

/*eslint max-statements:[2, 15], max-depth:[1, 2], complexity:[2, 5] */
 結果 
7:0 - Function 'englishToPigLatin' has a complexity of 7.
//englishToPigLatin 方法復雜度為 7
7:0 - This function has too many statements (16). Maximum allowed is 15.
// 次方法有太多聲明(16)。最大允許值為 15。
22:10 - Blocks are nested too deeply (5).
// 嵌套太深(5)
 重構 
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;
}
 重構后統計 

max-statements（最多聲明）: 16 → 6 
max-depth（最大嵌套）: 5 → 2 
complexity（復雜度）: 7 → 3 
max-len（最多行數）: 65 → 73 
max-params（最多參數）: 1 → 2 
max-nested-callbacks（最多嵌套回調）: 0 → 1 

資源 
jshint - http://jshint.com/

eslint - http://eslint.org/

jscomplexity - http://jscomplexity.org/

escomplex - https://github.com/philbooth/escomplex

jasmine - http://jasmine.github.io/ 
復制粘貼代碼的味道 
已有功能… 
 
已有代碼，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，現在想要這個功能 
 
于是，Duang! CIRCLE.JS 就出現了… 
// ... 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 ...
 為毛是這個味？因為我們復制粘貼了！ 
工具 
JSINSPECT 
檢查復制粘貼和結構相似的代碼 
一行命令： 
jsinspect
  
JSCPD 
程序源碼的復制 / 粘貼檢查器 
(JavaScript, TypeScript, C#, Ruby, CSS, SCSS, HTML, 等等都適用…) 
jscpd -f **/*.js -l 1 -t 30 --languages javascript
  
怎么能不被發現？重構 
把隨機顏色部分丟出去… 
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();
});
 再重構 
再把怪異的 [].forEach.call 部分丟出去… 
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();
});
 再再重構 
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');
 資源 

jsinspect 
jscpd 
CodePen 

switch 味道 
難聞的代碼 
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');
 為毛是這個味？違背“打開 / 關閉原則” 
增加個新形狀 
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;
}
 加點設計模式 
(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');
 再增加新形狀時 
// 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 || {}));
 還有其它的味道嗎？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 });
 神奇的字符串重構為對象類型 
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 });
 神奇字符重構為 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 規則 
規則 

no-switch – 不允許使用 switch 聲明 
no-complex-switch-case – 不允許使用復雜的 switch 聲明 

資源 

CodePen 
Addy Osmani’s JavaScript Design Patterns eBook 
ESLint 
eslint-plugin-smells 
ES6 Scoping 
ES6 Symbols 
Learn ES6 

this 深淵的味道 
難聞的代碼 
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);
 為什么是這個味？that 還是 self 還是 selfie 
替換方案

1) bind 
Person.prototype.brush = function() {
  this.teeth.forEach(function(tooth) {
    this.clean(tooth);
  }.bind(this));

  console.log('brushed');
};
 替換方案

2) forEach 的第二個參數 
Person.prototype.brush = function() {
  this.teeth.forEach(function(tooth) {
    this.clean(tooth);
  }, this);

  console.log('brushed');
};
 替換方案

3) ECMAScript 2015 (ES6) 
Person.prototype.brush = function() {
  this.teeth.forEach(tooth => {
    this.clean(tooth);
  });

  console.log('brushed');
};
 4a) 函數式編程 
Person.prototype.brush = function() {
  this.teeth.forEach(this.clean);

  console.log('brushed');
};
 4b) 函數式編程 
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 

字符串連接的味道 
難聞的代碼 
var build = function(id, href) {
  return $( "<div id='tab'><a href='" + href + "' id='"+ id + "'></div>" );
}
 為毛是這個味？因為字符串連接 
替換方案

@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);
}
 替換方案

2) ECMAScript 2015 (ES6) 模板字符串 
var build = (id, href) =>
  `<div id="tab"><a href="${href}" id="${id}"></div>`;
 替換方案

3) ECMAScript 2015 (ES6) 模板字符串 (多行) 
替換方案

4) 其它小型庫或大型庫 / 框架 

Lowdash 或 Underscore 
Angular 
React 
Ember 
等等… 

工具 
ESLINT-PLUGIN-SMELLS

no-complex-string-concat 
資源 
Tweet Sized JavaScript Templating Engine by @thomasfuchs

Learn ECMAScript 2015 (ES6) - http://babeljs.io/docs/learn-es6/ 
jQuery 調查 
難聞的代碼 
$(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');
});
 為毛是這個味？喪心病狂的鏈式調用 
愉快地重構吧 
// 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');
});
 最終 Demo 
工具 
ESLINT-PLUGIN-SMELLS 

no-complex-chaining 

難以琢磨的計時器 
難聞的代碼 
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;
}
 為毛這個味？無法同步的計時器 
Demo: setInterval 
用 setTimeout 保證順序 
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) {} */
 Demo: setTimeout 
重復定義 
難聞的代碼 
data = this.appendAnalyticsData(data);
data = this.appendSubmissionData(data);
data = this.appendAdditionalInputs(data);
data = this.pruneObject(data);
 替換方案

1) 嵌套調用函數 
data = this.pruneObject(
  this.appendAdditionalInputs(
    this.appendSubmissionData(
      this.appendAnalyticsData(data)
    )
  )
);
 2) forEach 
var funcs = [
  this.appendAnalyticsData,
  this.appendSubmissionData,
  this.appendAdditionalInputs,
  this.pruneObject
];

funcs.forEach(function(func) {
  data = func(data);
});
 3) reduce 
var funcs = [
  this.appendAnalyticsData,
  this.appendSubmissionData,
  this.appendAdditionalInputs,
  this.pruneObject
];

data = funcs.reduce(function(memo, func) {
  return func(memo);
}, data);
 4) flow 
data = _.flow(
  this.appendAnalyticsData,
  this.appendSubmissionData,
  this.appendAdditionalInputs,
  this.pruneObject
)(data);
 工具 
ESLINT-PLUGIN-SMELLS 

no-reassign 

資源 

forEach 
reduce 
_.flow 

過度耦合 
難聞的代碼 
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);
 為毛是這個味？緊密耦合的依賴關系 
如何改善！？！ 

依賴注入 
消息訂閱 
依賴注入 

function ShoppingCart() { this.items = []; }
ShoppingCart.prototype.addItem = function(item) {
  this.items.push(item);
};

function Product(name, shoppingCart) {
  this.name = name;
  this.shoppingCart = shoppingCart;
}
Product.prototype.addToCart = function() {
  this.shoppingCart.addItem(this);
};

var shoppingCart = new ShoppingCart();
var product = new Product('Socks', shoppingCart);
product.addToCart();
console.log(shoppingCart.items);
 
消息訂閱 

var channel = postal.channel();

function ShoppingCart() {
  this.items = [];
  channel.subscribe('shoppingcart.add', this.addItem);
}
ShoppingCart.prototype.addItem = function(item) {
  this.items.push(item);
};

function Product(name) { this.name = name; }
Product.prototype.addToCart = function() {
  channel.publish('shoppingcart.add', this);
};

var shoppingCart = new ShoppingCart();
var product = new Product('Socks');
product.addToCart();
console.log(shoppingCart.items);
 資源 

postal by @ifandelse 

連續不斷的交互 
難聞的代碼 
var search = document.querySelector('.Autocomplete');

search.addEventListener('input', function(e) {
  // Make Ajax call for autocomplete

  console.log(e.target.value);
});
 Demo: 根本停不下來 
解決方案：節流閥 
var search = document.querySelector('.Autocomplete');

search.addEventListener('input', _.throttle(function(e) {
  // Make Ajax call for autocomplete

  console.log(e.target.value);
}, 500));
 Demo 
解決方案：DEBOUNCE 
var search = document.querySelector('.Autocomplete');

search.addEventListener('input', _.debounce(function(e) {
  // Make Ajax call for autocomplete

  console.log(e.target.value);
}, 500));
 Demo 
資源 

lodash 
throttle 
debounce 

匿名函數 
難聞的代碼 
var search = document.querySelector('.Autocomplete');

search.addEventListener('input', function(e) {
  console.log(e.target.value);
});
 給函數命名的原因： 

堆棧追蹤 
去關聯 
代碼復用 
堆棧追蹤 

var search = document.querySelector('.Autocomplete');

search.addEventListener('input', function(e) {
  console.log(e.target.value);
});
  
修改后 
var search = document.querySelector('.Autocomplete');

search.addEventListener('input', function matches(e) {
  console.log(e.target.value);
});
  

去關聯 

單次事件綁定 
document.querySelector('button')
  .addEventListener('click', function handler() {
      alert('Ka-boom!');
    this.removeEventListener('click', handler);
  });
 Demo 

代碼復用 

var kaboom = function() { alert('Ka-boom'); };

document.querySelector('button').addEventListener('click', kaboom);

document.querySelector('#egg').addEventListener('mouseenter', kaboom);
 資源 

Chrome DevTools 

結尾 
更多的 ESLint 規則 

eslint-plugin-react 
eslint-plugin-angular 
eslint-plugin-ember 
eslint-plugin-backbone 

資源 
NPM 搜索 eslint-plugin
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JavaScript開發 JavaScript
去除 JavaScript 代碼的怪味

難聞的代碼

為毛是這個味？

很多原因：

檢查工具

重構

資源

復制粘貼代碼的味道

工具

怎么能不被發現？重構

資源

switch 味道

難聞的代碼

為毛是這個味？違背“打開 / 關閉原則”

還有其它的味道嗎？神奇的字符串

工具！？！

資源

this 深淵的味道

難聞的代碼

為什么是這個味？that 還是 self 還是 selfie

工具

字符串連接的味道

難聞的代碼

為毛是這個味？因為字符串連接

工具

資源

jQuery 調查

難聞的代碼

為毛是這個味？喪心病狂的鏈式調用

工具

難以琢磨的計時器

難聞的代碼

為毛這個味？無法同步的計時器

重復定義

難聞的代碼

工具

資源

過度耦合

難聞的代碼

為毛是這個味？緊密耦合的依賴關系

連續不斷的交互

難聞的代碼

匿名函數

難聞的代碼

資源

結尾

資源

相關經驗

相關資訊

相關文檔

目錄
