Error Handling in Javascript

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ERROR HANDLING MADE EASY JS VERSION

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Stratos Pavlakis Lead Engineer @Workable @th3hunt

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Error Handling

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Why bother?

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Why bother? Cause good error handling builds TRUST   between our users and our product

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Why bother? Cause good error handling builds TRUST   between our users and our product It IS part of the UX

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Why bother? Cause good error handling builds TRUST   between our users and our product It IS part of the UX

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errors for developers

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NullPointerException Java

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RxCocoa.RxCocoaURLError Swift

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e Javascript

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err Javascript

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InvalidLoginError Problem Domain

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errors for users?

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WHAT’S WRONG WITH THAT?

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– Younger self “Fix the copy and you’re set”

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Is that the case?

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Is that the case? Why do we keep getting this kind of   cryptic messages and bad UX? I asked at some point…

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WE DON’T DESIGN FOR ERROR

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Designing for errors

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DESIGNING FOR ERRORS what does that mean? Take #1

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DESIGNING FOR ERRORS MEANS… to anticipate errors!

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DESIGNING FOR ERRORS MEANS… ▸ List and identify them during design meetings to anticipate errors!

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DESIGNING FOR ERRORS MEANS… ▸ List and identify them during design meetings ▸ Getting the product team involved to anticipate errors!

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– Younger self “I got a solid theory… Let’s do this!”

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“In theory there is no difference between theory and practice…

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– Jan L. A. van de Snepscheut “In theory there is no difference between theory and practice… In practice there is.”

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A story of errors

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A story of errors inspired from true events

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A STORY OF ERRORS WALTER

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A STORY OF ERRORS WALTER ▸ Senior Engineer

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A STORY OF ERRORS WALTER ▸ Senior Engineer ▸ Anticipates all errors.

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A STORY OF ERRORS INSTANT BUY

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A STORY OF ERRORS INSTANT BUY Walter adds error handling an early feature of the web application.

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A STORY OF ERRORS INSTANT BUY Walter adds error handling an early feature of the web application. • Unauthenticated

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A STORY OF ERRORS INSTANT BUY Walter adds error handling an early feature of the web application. • Unauthenticated • Out of stock

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A STORY OF ERRORS INSTANT BUY Walter adds error handling an early feature of the web application. • Unauthenticated • Out of stock • CSRF

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A STORY OF ERRORS INSTANT BUY Walter adds error handling an early feature of the web application. • Unauthenticated • Out of stock • CSRF • Ofﬂine

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A STORY OF ERRORS INSTANT BUY Walter adds error handling an early feature of the web application. • Unauthenticated • Out of stock • CSRF • Ofﬂine • Unknown

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A STORY OF ERRORS INSTANT BUY instantBuy(item) .then(() => thanksForBuying(item)) .catch(error => { });

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A STORY OF ERRORS INSTANT BUY instantBuy(item) .then(() => thanksForBuying(item)) .catch(error => { });

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A STORY OF ERRORS INSTANT BUY instantBuy(item) .then(() => thanksForBuying(item)) .catch(error => { }); switch (error.status) { case 401: requestSignIn(); break;

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A STORY OF ERRORS INSTANT BUY instantBuy(item) .then(() => thanksForBuying(item)) .catch(error => { }); switch (error.status) { case 401: requestSignIn(); break; case 430: // CSRF promptToRefreshSession(); break; case 0: alert(`You seem to be offline. No worries…’); break; case 422: if (error.response === 'out of stock') { this.showOutOfStockDialog(); break; }

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A STORY OF ERRORS JESSE

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A STORY OF ERRORS JESSE ▸ Junior Engineer

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A STORY OF ERRORS JESSE ▸ Junior Engineer ▸ Hired 2 weeks ago

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A STORY OF ERRORS JESSE ▸ Junior Engineer ▸ Hired 2 weeks ago ▸ Anticipates no errors. At all!

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A STORY OF ERRORS SAVE FOR LATER

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A STORY OF ERRORS SAVE FOR LATER Jesse adds no error handling to the Nth feature of the web application… still 1st one for him.

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A STORY OF ERRORS SAVE FOR LATER

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A STORY OF ERRORS SAVE FOR LATER After a couple of code reviews, QA testing and a demo with bad WiFi

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A STORY OF ERRORS SAVE FOR LATER After a couple of code reviews, QA testing and a demo with bad WiFi • Unauthenticated

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A STORY OF ERRORS SAVE FOR LATER After a couple of code reviews, QA testing and a demo with bad WiFi • Unauthenticated • Out of stock

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A STORY OF ERRORS SAVE FOR LATER After a couple of code reviews, QA testing and a demo with bad WiFi • Unauthenticated • Out of stock • CSRF

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A STORY OF ERRORS SAVE FOR LATER After a couple of code reviews, QA testing and a demo with bad WiFi • Unauthenticated • Out of stock • CSRF • Ofﬂine

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A STORY OF ERRORS SAVE FOR LATER After a couple of code reviews, QA testing and a demo with bad WiFi • Unauthenticated • Out of stock • CSRF • Ofﬂine • Unknown

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A STORY OF ERRORS SAVE FOR LATER After a couple of code reviews, QA testing and a demo with bad WiFi • Unauthenticated • Out of stock • CSRF • Ofﬂine • Unknown with a twist - silently sync when online

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saveForLater(item) .catch(error => { A STORY OF ERRORS SAVE FOR LATER });

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saveForLater(item) .catch(error => { A STORY OF ERRORS });

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saveForLater(item) .catch(error => { A STORY OF ERRORS }); switch (error.status) { case 401: requestSignIn(); break;

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saveForLater(item) .catch(error => { A STORY OF ERRORS }); switch (error.status) { case 401: requestSignIn(); break; case 430: // CSRF promptToRefreshSession(); break;

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saveForLater(item) .catch(error => { A STORY OF ERRORS }); switch (error.status) { case 401: requestSignIn(); break; case 430: // CSRF promptToRefreshSession(); break; case 0: onlineTasks.push(() => saveForLater(item)); break; case 422: if (error.response === 'out of stock') { this.showOutOfStockDialog(); break; }

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saveForLater(item) .catch(error => { A STORY OF ERRORS copy-paste has a twist - swallow & send when online }); switch (error.status) { case 401: requestSignIn(); break; case 430: // CSRF promptToRefreshSession(); break; case 0: onlineTasks.push(() => saveForLater(item)); break; case 422: if (error.response === 'out of stock') { this.showOutOfStockDialog(); break; } default: alert('The operation is unavailable'); } logError(error);

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We end up with..

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We end up with.. Boilerplate, Repetition

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We end up with.. Boilerplate, Repetition No standard way of handling errors

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We end up with.. Boilerplate, Repetition No standard way of handling errors Cognitive overhead

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We end up with.. Boilerplate, Repetition No standard way of handling errors Cognitive overhead Inefficient error reporting

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We end up with.. Boilerplate, Repetition No standard way of handling errors Cognitive overhead Inefficient error reporting Friction in development cycles

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DESIGNING FOR ERRORS what does that mean? Take #2

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DESIGNING FOR ERRORS MEANS… (REVISED)

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DESIGNING FOR ERRORS MEANS… (REVISED) ▸ Anticipating errors

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DESIGNING FOR ERRORS MEANS… (REVISED) ▸ Anticipating errors ▸ Getting the product team involved

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DESIGNING FOR ERRORS MEANS… (REVISED) ▸ Anticipating errors ▸ Getting the product team involved ▸ Making error handling easy by engineering it

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DESIGNING FOR ERRORS checkpoint

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DESIGNING FOR ERRORS checkpoint what should guide our solution?

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DESIGNING FOR ERRORS KINDS OF ERRORS

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DESIGNING FOR ERRORS KINDS OF ERRORS - Business ‣ authentication ‣ validation ‣ stale data

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DESIGNING FOR ERRORS KINDS OF ERRORS - Business ‣ authentication ‣ validation ‣ stale data - Non business ‣ network ‣ storage ‣ device i/o (camera/mic/speakers/GPS) ‣ bugs

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DESIGNING FOR ERRORS KINDS OF ERRORS - Business ‣ authentication ‣ validation ‣ stale data - Non business ‣ network ‣ storage ‣ device i/o (camera/mic/speakers/GPS) ‣ bugs

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DESIGNING FOR ERRORS KINDS OF ERRORS - Business ‣ authentication ‣ validation ‣ stale data - Non business ‣ network ‣ storage ‣ device i/o (camera/mic/speakers/GPS) ‣ bugs cross-cut, common errors

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DESIGNING FOR ERRORS WE NEED ERROR HANDLING THAT IS… ▸ Present ▸ Shy ▸ Comprehensible ▸ Actionable ▸ Targeted ▸ Reportable

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DESIGNING FOR ERRORS WE NEED ERROR HANDLING THAT IS… ▸ Shy ▸ Comprehensible ▸ Actionable ▸ Targeted ▸ Reportable ▸ Is in place, timely and consistent

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DESIGNING FOR ERRORS WE NEED ERROR HANDLING THAT IS… ▸ Comprehensible ▸ Actionable ▸ Targeted ▸ Reportable ▸ Is in place, timely and consistent ▸ Communicates errors only if necessary

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DESIGNING FOR ERRORS WE NEED ERROR HANDLING THAT IS… ▸ Actionable ▸ Targeted ▸ Reportable ▸ Is in place, timely and consistent ▸ Communicates errors only if necessary ▸ Communicates errors in a comprehensible way

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DESIGNING FOR ERRORS WE NEED ERROR HANDLING THAT IS… ▸ Targeted ▸ Reportable ▸ Is in place, timely and consistent ▸ Communicates errors only if necessary ▸ Communicates errors in a comprehensible way ▸ Suggests how to resolve if possible

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DESIGNING FOR ERRORS WE NEED ERROR HANDLING THAT IS… ▸ Reportable ▸ Is in place, timely and consistent ▸ Communicates errors only if necessary ▸ Communicates errors in a comprehensible way ▸ Suggests how to resolve if possible ▸ Makes errors have the smallest area of effect

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DESIGNING FOR ERRORS WE NEED ERROR HANDLING THAT IS… ▸ Is in place, timely and consistent ▸ Communicates errors only if necessary ▸ Communicates errors in a comprehensible way ▸ Suggests how to resolve if possible ▸ Makes errors have the smallest area of effect ▸ Lets the product owners & engineers know

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and we need it to be easy

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and we need it to be easy easy as in …

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Error handling as easy as ordering a burger

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lettuce bun tomato bacon cheddar onion patty

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“Can I have a burger with baked flour, salted cured pork, relatively hard off-white natural cheese, tomato fruit and minced beef meat please?” - noone ever

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Instead we say… “The usual…” or “Cowboy burger with extra bacon without the onions”

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What we actually want

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✓ Natural language What we actually want

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✓ “offline” instead of “err.status === 0 || err.msg…” What we actually want

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✓ “offline” instead of “err.status === 0 || err.msg…” ✓ Presets of default actions for common errors What we actually want

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✓ “offline” vs “err.status === 0 || err.msg…” ✓ Presets of default actions for common errors ✓ Customise presets in a dynamic way ➡ Add actions ➡ Override actions ➡ Skip actions ➡ Log or… not What we actually want

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ErrorHandler A library that provides a declarative fluent API for flexible error handling

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ERROR HANDLER LET’S TAKE A LOOK ErrorHandler .build() .when(‘out-of-stock’, notifyOutOfStock) .when(‘unauthenticated’, promptForSignIn) .when(‘offline’, promptToRetry) .when(422, {type: ‘stale-pay-info’}, getPaymentInfo) .when(430, refreshCSRFToken) .when(err => err instanceof KaboomError, onKaboom) .whenNot('offline', sendToAnalytics) .always(enableSubmit) .logWith(new SentryLogger()) .handle(err);

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ERROR HANDLER BASIC API when(matcher, action) alias(name, matcher) when(alias, action) when(alias, options, action) whenNot(matcher, action) otherwise(action) always(action) logWith(logger)

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ERROR HANDLER BASIC API handle(err, options) run(function) retry()

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ERROR HANDLER BASIC API - ALIAS ErrorHandler .alias('offline', err => err.status === 0) ErrorHandler .alias( (tag) => typeof tag === 'number', (tag, err) => err.status === tag ) ErrorHandler .default() .when('offline', waitToGetOnline) .when(401, requestSignIn) .when(CustomError, onCustomError) .handle(err)

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ERROR HANDLER MOAAR API ErrorHandler .default() .when(‘foo', (err, handler) => { handleFoo(); handler.skipFollowing(); }) .when(err => err.match(/fo/), foHappened) .when('bar', (err, handler) => { handleBar(); handler.skipDefaults(); }) .when('validation', ‘max-length-exceeded‘, handleMaxLen) .when('validation', ‘profanity‘, handleProfanity) .when(KaboomError, kaboomHappened) .always(() => enableSubmitButton()) .logWith(new SentryLogger()) .run(submitLoginForm);

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Our strategy

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Our strategy Setup a default ErrorHandler once

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Our strategy Setup a default ErrorHandler once Customise the default ErrorHandler when needed based on the context

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Most of the time all we will need is… } catch (err) { } ErrorHandler.default().handle(err);

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and sometimes we need… } catch (err) { } ErrorHandler .default() .when(‘foo', onFoo) .when('bar', onBar) .handle(err);

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GANDALF APPROVES

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Back to our story

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saveForLater(item) .catch(error => { A STORY OF ERRORS copy-paste / default throughout the app has a twist }); switch (error.status) { case 401: requestSignIn(); break; case 430: // CSRF promptToRefreshSession(); break; case 0: onlineTasks.push(() => saveForLater(item)); break; case 422: if (error.response === 'out of stock') { this.showOutOfStockDialog(); break; } default: alert('The operation is unavailable'); } logError(error);

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turns to

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A STORY OF ERRORS ErrorHandler .default() .when('offline', () => { onlineTasks.push(() => saveForLater(item)); }) .handle(err); saveForLater(item) .catch(error => { });

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We get to.. Boilerplate, Repetition No standard way of handling Cognitive overhead Inefficient error reporting Friction in development cycles

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We get to.. No standard way of handling Cognitive overhead Inefficient error reporting Zero boilerplate, minimum repetition Friction in development cycles

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We get to.. Cognitive overhead Inefficient error reporting Zero boilerplate, minimum repetition Very standard way of handling errors Friction in development cycles

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We get to.. Inefficient error reporting Zero boilerplate, minimum repetition Very standard way of handling errors Readable domain related code Friction in development cycles

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We get to.. Zero boilerplate, minimum repetition Very standard way of handling errors Readable domain related code Efficient error tracking Friction in development cycles

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We get to.. Zero boilerplate, minimum repetition Very standard way of handling errors Readable domain related code Efficient error tracking One less problem to deal with

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– Swift Apprentice, Chapter 22 (Error Handling) “Error handling is the art of failing gracefully”

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Any Questions? No error you can’t .handle() Swift - https://github.com/Workable/swift-error-handler.git Java - https://github.com/Workable/java-error-handler.git Javascript - coming soon