How to Write Perfect Code with Standard and ESLint

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WRITE PERFECT CODE with Standard and ESLint

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npm install standard --save-dev

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THE END

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WRITE PERFECT CODE with Standard and ESLint

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What's a linter?

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A LINTER CATCHES BUGS

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What's a bug?

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WHEN YOUR CODE DOESN'T WORK

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“BUG”

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BUGBEAR BUGABOO BOOGEYMAN

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We could, for instance, begin with cleaning up our language by no longer calling a bug a bug but by calling it an error. — Edsger W. Dijkstra

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ESLINT Catches programmer errors

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JSLINT ➡ JSHINT ➡ ESLINT

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PROGRAMMER ERRORS BEST PRACTICES STYLE ISSUES

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CATCH PROGRAMMER ERRORS Shorten the Feedback Loop

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QUIZ: DO YOU SEE THE BUG IN THIS CODE? for (let i = 0; i < 10; i--) { console.log(i) }

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ENFORCE “FOR” LOOP UPDATE CLAUSE MOVING THE COUNTER IN THE RIGHT DIRECTION for (let i = 0; i < 10; i--) { // This loop never ends! } for (let i = 10; i >= 0; i++) { // This loop never ends! }

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DISALLOW ASSIGNMENT OPERATORS IN CONDITIONAL STATEMENTS if (user.jobTitle = 'manager') { // user.jobTitle is now incorrect }

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DISALLOW DUPLICATE ARGUMENTS IN FUNCTION DEFINITIONS function foo(a, b, a) { console.log('value of the second a:', a) }

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DISALLOW COMPARING TYPEOF EXPRESSIONS AGAINST INVALID STRINGS typeof foo === 'strnig' typeof foo === 'undefimed' typeof bar !== 'nunber' typeof bar !== 'fucntion'

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DISALLOW INVALID REGULAR EXPRESSION STRINGS IN REGEXP CONSTRUCTORS RegExp('[') RegExp('.', 'z') new RegExp('\\')

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Plus dozens more error checks

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How does one use ESLint?

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.ESLINTRC

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.ESLINTRC { "extends": ["standard"] } npm install eslint-config-standard --save-dev

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STANDARD VS. AIRBNB VS. GOOGLE

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.ESLINTRC { "extends": ["standard"], "rules": [ "quotes": ["error", "double"], "rest-spread-spacing": ["error", "always"], "semi": ["error", "always"] ] }

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WHY USE STANDARD?

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USE STANDARD $ npm install standard --save-dev $ standard Error: Use JavaScript Standard Style main.js:950:11: Expected '===' and instead saw '=='.

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VIBRANT COMMUNITY DOWNLOADED 1 MILLION TIMES PER MONTH EDITOR PLUGINS FOR EVERY MAJOR EDITOR BUILT INTO WEBSTORM

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PACKAGE.JSON { "name": "my-cool-package", "devDependencies": { "standard": "*" }, "scripts": { "test": "standard && node test.js" } }

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Should one use ESLint directly?

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BEWARE OF BIKESHEDDING

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BEWARE OF DUPLICATION

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PROGRAMMER ERRORS BEST PRACTICES STYLE ISSUES

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PROGRAMMER ERRORS BEST PRACTICES STYLE ISSUES

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QUIZ: WHAT DO THESE EXPRESSIONS EVALUATE TO? [] == false [] == ![] 3 == '03'

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QUIZ: WHAT DO THESE EXPRESSIONS EVALUATE TO? [] == false // true [] == ![] // true 3 == '03' // true

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REQUIRE === AND !== // NOT OK if (x == 42) { } // OK if (x === 42) { }

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STANDARD IS PRAGMATIC // OK if (x == null) { } // THE ABOVE IS EQUIVALENT TO... if (x === null || x === undefined) { }

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QUIZ: DO YOU SEE THE PROGRAMMER ERROR? hashOut.data = hashes + SSL_MD5_DIGEST_LEN; hashOut.length = SSL_SHA1_DIGEST_LEN; if ((err = SSLFreeBuffer(&hashCtx)) != 0) goto fail; if ((err = ReadyHash(&SSLHashSHA1, &hashCtx)) != 0) goto fail; if ((err = SSLHashSHA1.update(&hashCtx, &clientRandom)) != 0) goto fail; if ((err = SSLHashSHA1.update(&hashCtx, &serverRandom)) != 0) goto fail; if ((err = SSLHashSHA1.update(&hashCtx, &signedParams)) != 0) goto fail; goto fail; if ((err = SSLHashSHA1.final(&hashCtx, &hashOut)) != 0) goto fail; err = sslRawVerify(...);

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if ((err = SSLHashSHA1.update(&hashCtx, &signedParams)) != 0) goto fail; goto fail;

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if ((err = SSLHashSHA1.update(&hashCtx, &signedParams)) != 0) { goto fail; } goto fail;

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REQUIRE CURLY BRACE CONVENTIONS // NOT OK while (bar) baz() // NOT OK if (foo) { baz() } else qux()

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STANDARD IS PRAGMATIC // OK readFile(file, (err, data) => { if (err) throw err }) // OK readFile(file, (err, data) => { if (err) { throw err } })