JavaScript Refactoring

REFACTORING@szafranek

We form a wonderful community.Yet, we can learn a lot from other programming communities.

REFACTORING

Improvingthe design of codewithout changingits external behavior

Refactoring is not...If the changes affect external behavior, it’s rewriting, not refactoring.

Refactoring is not...For #1 excuse visit http://xkcd.com/303

continuous small stepsRefactoring should be done as a part of our every day workﬂow.Don’t wait for massive “big bang” refactorings.

InvestmentWhen to refactor?It’s an investment:- Makes change easier.- Helps ﬁnd bugs.But comes with time and effort cost.

enables you to go fasterMay make little sense just before a deadline.

makes code clear to other peopleNot machines

Martin Fowler“Any fool can write code that a computer can understand.Good programmers write code that humans can understand.”From the book “Refactoring”:http://www.amazon.com/Refactoring-Improving-Design-Existing-Code/dp/0201485672

;It’s much more important to write code that will be easy to understand by other peoplethan just understood by a browser.

clarity vsperformance

clarity enables performanceSome of you have heard that “Premature optimization is the root of all evil”.Its easier to optimize clean code than to clean up "optimized" code.

CODE SMELLS

Code is like cheese.Some people ﬁnd smelly what other ﬁnd deliciously wonderful.

duplicationIt makes change harder.The rule of 3: the third time you copy something, it’s time to refactor.

long methodsMore than 10 lines is long. This rule is arbitrary to force you to stop and think when youexceed this size.A method should do one thing!

switch/if statementsWhen they’re long and complex.

speculative codeRemove any code that “may be useful later”. You can always recover it from version control.Very often such code is NEVER nedeed and just confuses people who encounter it.

commentsComments become bad when used as a deodorant to hide messy code.

STEP #0

jslint jshintStatic analysis tools that detect mistakes and enforce clear style.Using lint was the single most important boost to my productivity in writing JS

John Carmack“Anything that isn’t crystal clear to a static analysis toolprobably isn’t clear to your fellow programmers”.From John Carmack’s great article on static analysis tools:http://altdevblogaday.com/2011/12/24/static-code-analysis/

STEP #1

UNIT TESTSTests give a safety net. How else do you know that you didn’t change the behavior?

JavaScript developer’s typical reaction to a question about unit tests

STEP #2Refactoring catalogue

What you learned about webstandards and clean front-end code is still valid. These are thebasics:* Separation of concerns.* Use CSS for styling.* Don’t inline JavaScript.* Assemble HTML in templates.

InfoMode.prototype.activate = function (config) { this.target = config.target; var entity = this.target.entity, entityName = entity.getProperName(), bulk = entity.getInfoModeString(), html = <h1> + entityName + </h1><div class=specification>{bulk}</div>, millisecondsStart, millisecondsTotal, millisecondsEnd, millisecondsLeft; if(entity.is(decoration)) { this.target.makeDynamic(); } this.infoPanel.innerHTML = ""; if(entity.contract) { millisecondsStart = entity.contractStartTime; millisecondsTotal = entity.contract.requiredTime; millisecondsEnd = (new Date()).getTime() - this.target.entity.contractStartTime; millisecondsLeft = millisecondsTotal-millisecondsEnd; if (entity.is(any house)) { if(this.target.entity.contractState === "started") { var gold = this.target.entity.getContractValue(); bulk = <div class="progress"><div style="width: 0%;"></div></div><p>Gives you + gold + coins in <span id="timeLeft">+utils.formatTime(millisecondsLeft)+</ span></p>; } else { bulk = bulk || <p>Please connect to road</p>; } } else if (entity.is(farm)) { var food = this.target.entity.getContractValue(); bulk = <div class="progress"><div style="width: 0%;"></div></div><p>Gives you + food + food in <span id="timeLeft">+utils.formatTime(millisecondsLeft)+</span></p>; } else if (entity.is(ship)) { if(this.target.entity.contractState === "started") { bulk = <div class="progress"><div style="width: 0%;"></div></div><p>Repair complete in <span id="timeLeft"> + utils.formatTime(millisecondsLeft) + </span></p>; } } } else {Real code, one method, ~150 lines. if(entity.is(castle)) { if(wooga.castle.playerData.upgradingCastle) { wooga.castle.CastleCompleteScreen.instance().show(); this.deactivate(); this.manager.setMode(wooga.castle.GameModesManager.Mode.BASIC); return; } bulk = <p><span class="population">Supported Population: + entity.definition.population

}; if(this.target.entity.contractState === "started") { var progress = document.querySelector(.progress div), timer = document.getElementById(timeLeft); progress.style.width = Math.floor((((new Date()).getTime() - millisecondsStart) / millisecondsTotal) * 100) + "%"; counter = setInterval(function () { var now = new Date().getTime(), timeFromStart = now - millisecondsStart; if((timeFromStart / millisecondsTotal) >= 1) { clearInterval(counter); } timer.innerHTML = utils.formatTime(millisecondsTotal - timeFromStart); progress.style.width = Math.floor((timeFromStart / millisecondsTotal) * 100) + "%"; }, 1000); } utils.publish(view:entity/focused, { "entity": entity, "entityView": entity.entityView, "infoMode": this }); //TODO move to pubsub // show boost info in influence area of decoration if (this.target instanceof wooga.castle.DecorationView) { this.target.entity.game.publish("decoration/showBoost", { entityView: this.target, x: this.target.entity.x, y: this.target.entity.y }); } // show boost of houses or farmfields in info mode if (this.target instanceof wooga.castle.FarmFieldView || this.target instanceof wooga.castle.HouseView) { if (this.target.entity.boost) { this.target.entity.entityView.showBoostInfo = true; } } this.show(); };Real code, one method, ~150 lines.

Extract method if(this.target.entity.contractState === "started") { var progress = document.querySelector(.progress div), timer = document.getElementById(timeLeft); progress.style.width = Math.floor((((new Date()).getTime() - millisecondsStart) / millisecondsTotal) * 100) + "%"; counter = setInterval(function () { var now = new Date().getTime(), timeFromStart = now - millisecondsStart; if((timeFromStart / millisecondsTotal) >= 1) { clearInterval(counter); } timer.innerHTML = utils.formatTime(millisecondsTotal - timeFromStart); progress.style.width = Math.floor((timeFromStart / millisecondsTotal) * 100) + "%"; }, 1000); } this.showProgressBar(startTime,requiredTime);Extract chunk that does one thing into a separate method.

Replace comments // show boost info in influence area of decoration if (this.target instanceof wooga.castle.DecorationView) { this.target.entity.game.publish("decoration/ showBoost", { entityView: this.target, x: this.target.entity.x, y: this.target.entity.y }); } this.showBoosts(entity);Well-named method makes comment unnecessary.

Remove duplicationif (this.target.entity.is("decoration")) { this.target.entity.game.publish("decoration/showBoost", { entityView: this.target, x: this.target.entity.x, y: this.target.entity.y });}var entity = this.target.entity;if (entity.is("decoration")) { entity.game.publish("decoration/showBoost", { entityView: this.target, x: entity.x, y: entity.y });}

Replace temp with a query var text = entity.getInfoModeString(); infoPanel.innerHTML = <div> + text + </div>; infoPanel.innerHTML = <div> + entity.getInfoModeString() + </div>;If temporary variable is used only once, it doesn’t make sense to introduce it.Sometimes even two calls don’t justify a temporary variable, unless they’re expensive and youwant to cache the results.

Remove speculative codeswitch (action) { case "move": break; case "destroy": break; default: break;}

Use meaningful names var p = this.current.params; var r = this.current.results; if (r.restProduct) { p.query = r.restProduct; } var params = this.current.params; var results = this.current.results; if (results.restProduct) { params.query = results.restProduct; }There are 2 hard things in CS: “cache invalidation and naming things”.Leave compression to miniﬁers!

Use polymorphism if (entity.is(house)) { if(entity.contractState === "started") { var gold = entity.getContractValue(); bulk = <p>Gives you + gold + coins</p>; } else { bulk = bulk || <p>Please connect to road</p>; } } else if (entity.is(farm)) { var food = entity.getContractValue(); bulk = <p>Gives you + food + food</p>; } else if (entity.is(ship)) { bulk = <p>Repair complete in + time + </span></p>; } var bulk = entity.getInfoModeString();Each entity class implements its own version of the method.

this.target = config.target; var entity = this.target.entity, entityName = entity.getProperName(), bulk = entity.getInfoModeString(), html = <h1> + entityName + </h1><div class=specification>{bulk}</div>, millisecondsStart, millisecondsTotal, millisecondsEnd, millisecondsLeft; if(entity.is(decoration)) { this.target.makeDynamic(); } this.infoPanel.innerHTML = ""; if(entity.contract) { millisecondsStart = entity.contractStartTime; millisecondsTotal = entity.contract.requiredTime; millisecondsEnd = (new Date()).getTime() - this.target.entity.contractStartTime; millisecondsLeft = millisecondsTotal-millisecondsEnd; if (entity.is(any house)) { if(this.target.entity.contractState === "started") { var gold = this.target.entity.getContractValue(); bulk = <div class="progress"><div style="width: 0%;"></div></div><p>Gives you + gold + coins in <span id="timeLeft">+utils.formatTime(millisecondsLeft)+</span></ p>; } else { bulk = bulk || <p>Please connect to road</p>; } } else if (entity.is(farm)) { var food = this.target.entity.getContractValue(); bulk = <div class="progress"><div style="width: 0%;"></div></div><p>Gives you + food + InfoMode.prototype.activate = function (config) { food in <span id="timeLeft">+utils.formatTime(millisecondsLeft)+</span></p>; this.target = config.target; } else if (entity.is(ship)) { if(this.target.entity.contractState === "started") { var entity = this.target.entity; bulk = <div class="progress"><div style="width: 0%;"></div></div><p>Repair complete in <span id="timeLeft"> + if (entity.is(castle) && wooga.castle.playerData.upgradingCastle) { utils.formatTime(millisecondsLeft) + </span></p>; } wooga.castle.CastleCompleteScreen.instance().show(); } this.deactivate(); this.manager.setMode(wooga.castle.GameModesManager.Mode.BASIC); } else { return; if(entity.is(castle)) { } if(wooga.castle.playerData.upgradingCastle) { wooga.castle.CastleCompleteScreen.instance().show(); if (entity.is(decoration)) { this.deactivate(); this.target.makeDynamic(); this.manager.setMode(wooga.castle.GameModesManager.Mode.BASIC); } return; } this.infoPanel.innerHTML = <h1> + entity.getProperName() + </h1><div bulk = <p><span class="population">Supported Population: + class=specification> + entity.getInfoModeString() + </div>; entity.definition.population + </span></p>; } else if(entity.is(decoration)) { // RADAR: [szafranek] Why is this HERE? Moving it to worldView and listening to "entity/focused" looks better to me. bulk = <p>Nearby buildings get a ; var concatBoosts = false; this.manager.view.isFocusedEntityView = function (entityView) { if (entity.definition.goldBoost) { return entityView === config.target; bulk += gold boost of + entity.definition.goldBoost + %; }; concatBoosts = true; } if (entity.definition.foodBoost) { if (entity.contractState === wooga.castle.House.ContractState.STARTED) { if(concatBoosts) { this.showProgressBar(entity.contractStartTime, bulk += </p><p>and a ; } entity.contract.requiredTime); bulk += food boost of + entity.definition.foodBoost + %.; } else if (entity.contractState === } wooga.castle.House.ContractState.CONSTRUCTION) { } this.showProgressBar(entity.constructionStartTime, } entity.contract.constructionTime); } this.infoPanel.innerHTML = html.replace({bulk}, bulk); this.manager.view.isFocusedEntityView = function (entityView) { utils.publish(view:entity/focused, { return entityView === config.target; "entity": entity, }; "entityView": entity.entityView, if(this.target.entity.contractState === "started") { "infoMode": this var progress = document.querySelector(.progress div), }); timer = document.getElementById(timeLeft); progress.style.width = Math.floor((((new Date()).getTime() - millisecondsStart) / millisecondsTotal) * 100) + "%"; this.showBoosts(entity); counter = setInterval(function () { var now = new Date().getTime(), timeFromStart = now - millisecondsStart; this.show(); if((timeFromStart / millisecondsTotal) >= 1) { clearInterval(counter); }; } timer.innerHTML = utils.formatTime(millisecondsTotal - timeFromStart); progress.style.width = Math.floor((timeFromStart / millisecondsTotal) * 100) + "%"; }, 1000); } utils.publish(view:entity/focused, { "entity": entity, "entityView": entity.entityView, "infoMode": this }); //TODO move to pubsub // show boost info in influence area of decoration if (this.target instanceof wooga.castle.DecorationView) { this.target.entity.game.publish("decoration/showBoost", { entityView: this.target, x: this.target.entity.x, y: this.target.entity.y }); } // show boost of houses or farmfields in info mode if (this.target instanceof wooga.castle.FarmFieldView || this.target instanceof wooga.castle.HouseView) { if (this.target.entity.boost) { this.target.entity.entityView.showBoostInfo = true; } } this.show();Original method after refactoring. };

Know where to stop.Ask yourself: is the further investment wortwhile?

LEARNING MORE

RefactoringMartin Fowler

coderetreat.orgOrganize one yourself if there’s none in your city!

Robert C. Martin“Learning to write clean code is hard work.It requires more than just the knowledge of principles and patterns.You must sweat over it. You must practice it yourself, and watch yourself fail.You must watch others practice it and fail.”From the book “Clean Code”:http://www.amazon.com/Clean-Code-Handbook-Software-Craftsmanship/dp/0132350882

Write code for peopleLearn from others@szafranek

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JavaScript Refactoring

by Krzysztof Szafranek on Apr 28, 2012

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