Squashing JavaScript Bugs

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SQUASHING JavaScript Bugs with Todd H Gardner @toddhgardner

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AGENDA 1. About JavaScript 2. How to fix Bugs 3. Fix Some Bugs 4. Fix More Bugs 5. Design for Debuggability with Todd H Gardner @toddhgardner

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TITANIUM SPONSORS Platinum Sponsors Gold Sponsors

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Are you ready to play?

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''.length C: 2 What will the following JavaScript code return? 1 D: A: undefined B: 1

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''.length C: 2 1 D: A: undefined B: 1 String.prototype.length returns the number of bytes rather than the number of characters. Unicode characters, like emoji, require two bytes.

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0.1 + 0.2 C: 0.3000000000004 What will the following JavaScript code return? 2 D: ‘0.3’ A: 0.3 B: 0.2999999999997

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2 JavaScript's floating point operations have issues with overflow rounding precision. 0.1 + 0.2 C: 0.3000000000004 D: ‘0.3’ A: 0.3 B: 0.2999999999997

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new Date(2016, 5, 31) C: 2016 May 31 What will the following JavaScript code return? 3 D: 2017 May 31 A: 2016 July 1 B: 2016 June 31

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3 Months are zero based in Date. This specifies June 31, which overflows to July 1. new Date(2016, 5, 31) C: 2016 May 31 D: 2017 May 31 A: 2016 July 1 B: 2016 June 31

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new Array(0, 1, Array(2)); C: [0, 1, [object Array]] What will the following JavaScript code return? 4 D: [0, 1, [undefined, undefined]] A: [0, 1, [2]] B: [0, 1, 2]

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4 Instantiating an Array with multiple arguments creates an Array from those values. However a single argument only specifies the length. new Array(0, 1, Array(2)); C: [0, 1, [object Array]] D: [0, 1, [undefined, undefined]] A: [0, 1, [2]] B: [0, 1, 2]

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[10, 5, 1].sort() C: [1, 10, 5] What will the following JavaScript code return? 5 D: [5, 10, 1] A: [1, 5, 10] B: [10, 5, 1]

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5 Array.prototype.sort's default comparator assumes String operations. All values are coerced and compared as Strings. [10, 5, 1].sort() C: [1, 10, 5] D: [5, 10, 1] A: [1, 5, 10] B: [10, 5, 1]

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WINNER

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JavaScript Happens

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Debugging is like being the detective in a crime movie where you're also the murderer “ Filipe Fortes

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Identify Isolate Resolve Prevent How To Fix Bugs

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Identify Isolate Resolve Prevent • Development • Testing • Monitoring • User Reports

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Identify Isolate Resolve Prevent • Development • Testing • Monitoring • User Reports cheaper, better, faster

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• Context Identify Isolate Resolve Prevent - Browser - Page - User - Script(s)

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• Timeline Identify Isolate Resolve Prevent Complex State Machine - API(s) - JS App(s) - DOM - Browser

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• Root Cause Identify Isolate Resolve Prevent - Symptoms - State

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• Context • Timeline • Root Cause Identify Isolate Resolve Prevent

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Identify Isolate Resolve Prevent Application Code Browser API DOM Network Services

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Identify Isolate Resolve Prevent Application Code Browser API DOM Network Services Your level of Control

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Identify Isolate Resolve Prevent Risk, Change, Impact, & “The Right Way”

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Identify Isolate Resolve Prevent • Regression Tests Test to check for the recurrence of a bug

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Identify Isolate Resolve Prevent • Process Change - Manual - Automated

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Identify Isolate Resolve Prevent • Do Nothing Tests and Process have cost. Don’t increase them trivially.

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Identify Isolate Resolve Prevent • Regression Tests • Process • Do Nothing

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AGENDA 1. About JavaScript 2. How to fix Bugs 3. Fix Some Bugs 4. Fix More Bugs 5. Design for Debuggability with Todd H Gardner @toddhgardner

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XKCD.com

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getRANTr introducing

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BUGS BECAUSE JAVASCRIPT

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37,000,000,000 thousands millions billions ones I’ve helped fix JavaScript Bugs {Track:js} JavaScript Error Monitoring

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github.com / toddhgardner / getRANTR getRANTr

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Backbone.SOMETHING.extend({ // all our stuff is here });

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The fewest number of concepts possible Code Review

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QA Identified Bug: User cannot delete a rant from their timeline. Think twice, rant once. 1

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KILL IT! 1 AHHHHHHH!!!!

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Your Turn 1 Exercise 1

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Logical Bug • Event PreventDefault • Function context 1

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1 Concepts: • “Keystone” Users • DOM Inspector • Async Callstacks

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2 User Identified Bug: Rant text remembered after deleted. Is it paranoia if “they” are actually after you?

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KILL IT! 2 AHHHHHHH!!!!

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Your Turn 2 Exercise 2

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Logical Bug • Empty String • Falsy 2

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2 Concepts: • Application (Storage) Explorer • Breaking Execution

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3 Monitoring Identified Bug: Server reporting lots of 400 Requests. Bad Request? I’ll request what I want.

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3 AJAX Error POST 400 Bad Request /api/rants/ User Click User Input 0 characters

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KILL IT! 3 AHHHHHHH!!!!

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Your Turn 3 Exercise 3

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Data Bug • User-Form Validation 3

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3 Concepts: • Network Inspector • Response Previews • JavaScript Debugger

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4 Monitoring Identified Bug: Singular user generating lots of errors Sucks to be them

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Cannot read ’substr’ of null 4

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KILL IT! 4 AHHHHHHH!!!!

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Your Turn 4 Exercise 4

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Data Bug • Invalid datatypes from server • Safety-checking data 4

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4 Concepts: • Network Inspector • Response Previews • JavaScript Debugger

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AGENDA 1. About JavaScript 2. How to fix Bugs 3. Fix Some Bugs 4. Fix More Bugs 5. Design for Debuggability with Todd H Gardner @toddhgardner

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Are you ready to play?

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Math.max() C: NaN What will the following JavaScript code return? 1 D: 10e25678 A: Infinity B: -Infinity

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1 Called with no arguments, Math.max() returns the smallest number in JavaScript. Math.max() C: NaN D: 10e25678 A: Infinity B: -Infinity

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(function foo(a, b) {}).length C: 2 What will the following JavaScript code return? 2 D: 21 A: undefined B: 0

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2 Function.prototype.length returns the number of arguments specified in the function definition. (function foo(a, b) {}).length C: 2 D: 21 A: undefined B: 0

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+"42" C: “43” What will the following JavaScript code return? 3 D: NaN A: 42 B: 43

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3 'The "+" operator is not preceded by a String, so it is considered arithmetic and attempts to coerce the following value into a Number. The gets evaluated as "0 + 42". +"42" C: “43” D: NaN A: 42 B: 43

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'' - '' C: What will the following JavaScript code return? 4 D: NaN A: '' B: ''

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4 '' - '' C: D: NaN A: '' B: '' The "-" operator is always arithmetic, so both items are coerced into Numbers. They cannot be interpreted, and result in NaN.

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!!"" C: true 5 D: false A: “” B: JavaScript's Number type includes the concepts of positive and negative Infinity.

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!!"" C: true What will the following JavaScript code return? 5 D: false A: “” B:

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WINNER

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AGENDA 1. About JavaScript 2. How to fix Bugs 3. Fix Some Bugs 4. Fix More Bugs 5. Design for Debuggability with Todd H Gardner @toddhgardner

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5 Developer Identified Bug: Unexpectedly high memory usage. You’ve got 16GB! What else are you going to do with it?

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KILL IT! 5 AHHHHHHH!!!!

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Your Turn 5 Exercise 5

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Memory Bug • Unreleased Objects • Orphaned DOM Trees 5

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5 Concepts: • Profiler • Timeline

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6 User Identified Bug: Sometimes slow to load the page. Like you have something better to do?

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KILL IT! 6 AHHHHHHH!!!!

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Your Turn 6 Exercise 6

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Performance Bug • Blocking Assets • Uncompressed Assets 6

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6 Concepts: • Timeline • Network Preview

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Monitoring Identified Bug: form.submit is not a function on signup Who would signup for this stupid service anyway? 7

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KILL IT! 7 AHHHHHHH!!!!

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Your Turn 7 Exercise 7

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3rd-Party Bug • Uncontrolled Changes 7

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7 Concepts: • External Risk • DOM Inconsistency

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8 Monitoring Identified Bug: “analytics is not defined” Sounds like a PEBKAC to me. Send them an id-10-t cable. “$ is not defined”

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KILL IT! 8 AHHHHHHH!!!!

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Your Turn 8 Exercise 8

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Network/Proxy Bug • Poor networks • Active blocking 8

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8 Concepts: • Load Checking • Simulating Networks • Charles/Fiddler Proxy

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AGENDA 1. About JavaScript 2. How to fix Bugs 3. Fix Some Bugs 4. Fix More Bugs 5. Design for Debuggability with Todd H Gardner @toddhgardner

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The web is the most hostile software engineering environment imaginable -- Douglas Crockford “

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Identify Isolate Resolve Prevent Design for Debuggability

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Identify Isolate Resolve Prevent • Development • Testing • Monitoring • User Reports cheaper, better, faster

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Identify Isolate Resolve Prevent Monitoring {Track:js} JavaScript Error Monitoring elastic

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Identify Isolate Resolve Prevent setTimeout(function() { if (!HAS_LOADED_CONDITION) { trackError('slow load'); } }, 10000); Instrument

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Simplicity Identify Isolate Resolve Prevent

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Duplication Abstraction Identify Isolate Resolve Prevent

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Rule of 3 Identify Isolate Resolve Prevent

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DOM Identify Isolate Resolve Prevent Network Browser API Application Code

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Identify Isolate Resolve Prevent Gary Bernhardt Destroy All Software

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Design for Test (hardware) Identify Isolate Resolve Prevent

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Debug Mode http://myapp.com?debug Identify Isolate Resolve Prevent

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Identify Isolate Resolve Prevent Tools {Track:js}

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Identify Isolate Resolve Prevent Lower the Risk of Change

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Identify Isolate Resolve Prevent • Regression Tests • Update Process • Do Nothing Think

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Identify Isolate Resolve Prevent Bug Count as a proxy for Design Quality

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Identify Isolate Resolve Prevent The Doer- thinger The Enterprise- Ready Cylinder The all- powerful cloud Widgetizer Requests Generic Architecture

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Identify Isolate Resolve Prevent The Doer- thinger The Enterprise- Ready Cylinder The all- powerful cloud Widgetizer Requests Generic Architecture 51 2 7 0 Bug Count

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Identify Isolate Resolve Prevent Design for Debuggability

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AGENDA 1. About JavaScript 2. How to fix Bugs 3. Fix Some Bugs 4. Fix More Bugs 5. Design for Debuggability with Todd H Gardner @toddhgardner