[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"me":3,"catalog:en:frontend\u002Ftypescript-narrowing-control-flow":4,"config":234},null,{"field_key":5,"field_name":6,"seniority":7,"topic_key":8,"topic_name":9,"spec_key":7,"spec_name":7,"locale":10,"cell_total":11,"field_total":12,"seniorities":13,"topics":17,"specs":133,"samples":150},"frontend","Frontend","","typescript-narrowing-control-flow","Typescript Narrowing Control Flow","en",75,2925,[14,15,16],"junior","mid","senior",[18,21,24,27,30,33,36,39,42,45,48,51,54,57,60,63,66,69,72,75,78,81,84,87,90,93,96,99,102,105,106,109,112,115,118,121,124,127,130],{"key":19,"name":20,"count":11},"accessibility","Accessibility",{"key":22,"name":23,"count":11},"angular-change-detection","Angular Change Detection",{"key":25,"name":26,"count":11},"angular-components-lifecycle","Angular Components Lifecycle",{"key":28,"name":29,"count":11},"angular-dependency-injection","Angular Dependency Injection",{"key":31,"name":32,"count":11},"angular-directives-pipes","Angular Directives Pipes",{"key":34,"name":35,"count":11},"angular-router-forms","Angular Router Forms",{"key":37,"name":38,"count":11},"angular-testing-performance","Angular Testing Performance",{"key":40,"name":41,"count":11},"css-layout","Css Layout",{"key":43,"name":44,"count":11},"dom-browser-apis","Dom Browser Apis",{"key":46,"name":47,"count":11},"javascript-async-concurrency","Javascript Async Concurrency",{"key":49,"name":50,"count":11},"javascript-language","Javascript Language",{"key":52,"name":53,"count":11},"javascript-memory-performance","Javascript Memory Performance",{"key":55,"name":56,"count":11},"javascript-modules-bundling","Javascript Modules Bundling",{"key":58,"name":59,"count":11},"javascript-prototypes-oop","Javascript Prototypes Oop",{"key":61,"name":62,"count":11},"javascript-runtime-apis","Javascript Runtime Apis",{"key":64,"name":65,"count":11},"javascript-testing-tooling","Javascript Testing Tooling",{"key":67,"name":68,"count":11},"performance","Performance",{"key":70,"name":71,"count":11},"react-components-jsx","React Components Jsx",{"key":73,"name":74,"count":11},"react-context-state","React Context State",{"key":76,"name":77,"count":11},"react-effects-lifecycle","React Effects Lifecycle",{"key":79,"name":80,"count":11},"react-forms-suspense","React Forms Suspense",{"key":82,"name":83,"count":11},"react-hooks-state","React Hooks State",{"key":85,"name":86,"count":11},"react-rendering-performance","React Rendering Performance",{"key":88,"name":89,"count":11},"rendering-reactivity","Rendering Reactivity",{"key":91,"name":92,"count":11},"state-management","State Management",{"key":94,"name":95,"count":11},"testing","Testing",{"key":97,"name":98,"count":11},"typescript-advanced-types","Typescript Advanced Types",{"key":100,"name":101,"count":11},"typescript-generics","Typescript Generics",{"key":103,"name":104,"count":11},"typescript-modules-declarations","Typescript Modules Declarations",{"key":8,"name":9,"count":11},{"key":107,"name":108,"count":11},"typescript-tooling-config","Typescript Tooling Config",{"key":110,"name":111,"count":11},"typescript-type-fundamentals","Typescript Type Fundamentals",{"key":113,"name":114,"count":11},"vue-components-props","Vue Components Props",{"key":116,"name":117,"count":11},"vue-composition-api","Vue Composition Api",{"key":119,"name":120,"count":11},"vue-directives-templates","Vue Directives Templates",{"key":122,"name":123,"count":11},"vue-performance-testing","Vue Performance Testing",{"key":125,"name":126,"count":11},"vue-reactivity-system","Vue Reactivity System",{"key":128,"name":129,"count":11},"vue-router-state-management","Vue Router State Management",{"key":131,"name":132,"count":11},"web-security","Web Security",[134,138,141,144,147],{"key":135,"name":136,"count":137},"angular","Angular",450,{"key":139,"name":140,"count":137},"javascript","JavaScript",{"key":142,"name":143,"count":137},"react","React",{"key":145,"name":146,"count":137},"typescript","TypeScript",{"key":148,"name":149,"count":137},"vue","Vue",[151,169,182,195,208,221],{"id":152,"topic":9,"difficulty":153,"body":154,"options":155,"correct_key":160,"explanation":168},"019f7611-bd36-73fd-996d-ece7b516a32b",1,"In TypeScript, what does a `typeof x === \"string\"` check inside an `if` block do to the type of `x` for the rest of that block?",[156,159,162,165],{"key":157,"text":158},"a","Nothing — TypeScript never changes a variable's type based on runtime checks",{"key":160,"text":161},"b","Narrows `x`'s type to `string` for the rest of that block",{"key":163,"text":164},"c","Converts `x` to a `string` at runtime, changing its actual value",{"key":166,"text":167},"d","Removes the type annotation from `x` entirely","This is TypeScript's core narrowing mechanism: a `typeof` check is one of several recognized type guards. Inside the branch where the check is true, the compiler statically narrows the variable's type to `string` for all code within that block, so string-only methods become available without a cast.",{"id":170,"topic":9,"difficulty":153,"body":171,"options":172,"correct_key":163,"explanation":181},"019f7611-bd37-71e3-8149-af5fbe2733c4","```typescript\nclass Dog { bark(): void {} }\nclass Cat { meow(): void {} }\n\nfunction speak(pet: Dog | Cat) {\n  if (pet instanceof Dog) {\n    pet.bark();\n  } else {\n    pet.meow();\n  }\n}\n```\nDoes this compile without error?",[173,175,177,179],{"key":157,"text":174},"No — `instanceof` cannot be used to narrow a union of two classes",{"key":160,"text":176},"No — `pet.meow()` is unreachable and TypeScript flags it as an error",{"key":163,"text":178},"Yes — `instanceof` narrows `pet` to `Cat` in the `else` branch, so `meow()` is valid",{"key":166,"text":180},"Yes, but only if both classes share a common base class","`instanceof` is a standard narrowing guard. In the `if` branch, `pet` narrows to `Dog`, so `bark()` is valid. Since the union has only two members, TypeScript can conclude the `else` branch means `pet` must be `Cat`, narrowing it accordingly — no shared base class is required.",{"id":183,"topic":9,"difficulty":153,"body":184,"options":185,"correct_key":157,"explanation":194},"019f7611-bd37-7c16-a60c-16341f2fc162","```typescript\nfunction total(value: number | number[]) {\n  if (Array.isArray(value)) {\n    return value.reduce((a, b) => a + b, 0);\n  }\n  return value * 2;\n}\n```\nWhat does `Array.isArray(value)` do for the type of `value` inside the `if` block?",[186,188,190,192],{"key":157,"text":187},"Narrows `value` to `number[]`, so array methods like `reduce` are valid",{"key":160,"text":189},"Has no effect on the type; a manual cast is still required to call `reduce`",{"key":163,"text":191},"Narrows `value` to `any[]`, losing the `number` element type",{"key":166,"text":193},"Only works at runtime and causes a compile error on `reduce`","`Array.isArray` is a built-in type guard recognized by TypeScript. Inside the `if` block it narrows `value` from `number | number[]` down to `number[]`, so array methods are usable directly with full type information (elements are known to be `number`).",{"id":196,"topic":9,"difficulty":153,"body":197,"options":198,"correct_key":166,"explanation":207},"019f7611-bd38-7691-945c-bc177ea03ca4","```typescript\nfunction greet(name: string | undefined) {\n  if (name) {\n    console.log(name.toUpperCase());\n  }\n}\n```\nInside the `if` block, what is the narrowed type of `name`?",[199,201,203,205],{"key":157,"text":200},"`string | undefined`, unchanged",{"key":160,"text":202},"`undefined`",{"key":163,"text":204},"`unknown`",{"key":166,"text":206},"`string`","A plain truthiness check (`if (name)`) is a recognized narrowing pattern: it excludes falsy values, which for `string | undefined` means excluding `undefined` (and the empty string `\"\"`, though that doesn't remove a type here). The remaining type inside the block is `string`.",{"id":209,"topic":9,"difficulty":153,"body":210,"options":211,"correct_key":160,"explanation":220},"019f7611-bd39-714e-9305-1ceddc48efc7","```typescript\ntype Cat = { meow(): void };\ntype Robot = { beep(): void };\n\nfunction activate(entity: Cat | Robot) {\n  if (\"meow\" in entity) {\n    entity.meow();\n  } else {\n    entity.beep();\n  }\n}\n```\nWhat narrows `entity` to `Cat` in the `if` branch?",[212,214,216,218],{"key":157,"text":213},"TypeScript cannot narrow object-type unions this way; this is a compile error",{"key":160,"text":215},"The `in` operator, checking whether the `\"meow\"` property exists on the object's type",{"key":163,"text":217},"TypeScript infers it from the variable's name `entity`",{"key":166,"text":219},"It only works because `Cat` and `Robot` both have exactly one method","The `in` operator is a recognized narrowing guard for object types: `\"prop\" in obj` checks, at the type level, which union member(s) declare that property. Since only `Cat` has `meow`, TypeScript narrows `entity` to `Cat` in the `if` branch and to `Robot` in the `else`.",{"id":222,"topic":9,"difficulty":153,"body":223,"options":224,"correct_key":163,"explanation":233},"019f7611-bd39-7d0f-8e3c-5a1ee6e85cd0","A function accepts `id: string | number` and needs to call `.toFixed(2)`, which only exists on `number`. What is the correct way to make this compile?",[225,227,229,231],{"key":157,"text":226},"Cast `id` to `number` with `as number` without checking anything first",{"key":160,"text":228},"Call `.toFixed(2)` directly; TypeScript will auto-convert `string` at runtime",{"key":163,"text":230},"Check `typeof id === \"number\"` first, then call `.toFixed(2)` inside that branch",{"key":166,"text":232},"Change the parameter type to `any` so all method calls are allowed","The idiomatic approach is a type guard: `typeof id === \"number\"` narrows `id` to `number` inside that branch, making `.toFixed(2)` valid without a cast. Blind casting (`as number`) suppresses the check instead of proving it, and `any` throws away type safety entirely.",{"fields":235,"seniorities":410,"interview_shapes":411,"locales":416,"oauth":418,"question_count":421,"coach_enabled":422,"jd_match_enabled":422},[236,261,270,287,311,324,343,362,384,391,397,404],{"key":237,"name_tr":238,"name_en":238,"sort":153,"specializations":239},"backend","Backend",[240,243,246,249,252,255,258],{"key":241,"name":242,"field":237},"general","Genel",{"key":244,"name":245,"field":237},"go","Go",{"key":247,"name":248,"field":237},"python","Python",{"key":250,"name":251,"field":237},"java","Java",{"key":253,"name":254,"field":237},"csharp","C#\u002F.NET",{"key":256,"name":257,"field":237},"nodejs","Node.js",{"key":259,"name":260,"field":237},"php","PHP",{"key":5,"name_tr":6,"name_en":6,"sort":262,"specializations":263},2,[264,265,266,267,268,269],{"key":241,"name":242,"field":5},{"key":139,"name":140,"field":5},{"key":145,"name":146,"field":5},{"key":142,"name":143,"field":5},{"key":148,"name":149,"field":5},{"key":135,"name":136,"field":5},{"key":271,"name_tr":272,"name_en":272,"sort":273,"specializations":274},"fullstack","Fullstack",3,[275,276,277,278,279,280,281,282,283,284,285,286],{"key":241,"name":242,"field":271},{"key":244,"name":245,"field":237},{"key":247,"name":248,"field":237},{"key":250,"name":251,"field":237},{"key":253,"name":254,"field":237},{"key":256,"name":257,"field":237},{"key":259,"name":260,"field":237},{"key":139,"name":140,"field":5},{"key":145,"name":146,"field":5},{"key":142,"name":143,"field":5},{"key":148,"name":149,"field":5},{"key":135,"name":136,"field":5},{"key":288,"name_tr":289,"name_en":289,"sort":290,"specializations":291},"devops-cloud","DevOps \u002F Cloud",4,[292,293,296,299,302,305,308],{"key":241,"name":242,"field":288},{"key":294,"name":295,"field":288},"aws","AWS",{"key":297,"name":298,"field":288},"gcp","GCP",{"key":300,"name":301,"field":288},"azure","Azure",{"key":303,"name":304,"field":288},"kubernetes","Kubernetes",{"key":306,"name":307,"field":288},"terraform","Terraform",{"key":309,"name":310,"field":288},"linux","Linux",{"key":312,"name_tr":313,"name_en":313,"sort":314,"specializations":315},"ai-engineer","AI Engineer",5,[316,317,318,321],{"key":241,"name":242,"field":312},{"key":247,"name":248,"field":312},{"key":319,"name":320,"field":312},"llm-rag","LLM\u002FRAG",{"key":322,"name":323,"field":312},"mlops","MLOps",{"key":325,"name_tr":326,"name_en":327,"sort":328,"specializations":329},"database","Veritabanı","Database",6,[330,331,334,337,340],{"key":241,"name":242,"field":325},{"key":332,"name":333,"field":325},"postgresql","PostgreSQL",{"key":335,"name":336,"field":325},"mysql","MySQL",{"key":338,"name":339,"field":325},"mongodb","MongoDB",{"key":341,"name":342,"field":325},"redis","Redis",{"key":344,"name_tr":345,"name_en":346,"sort":347,"specializations":348},"mobile","Mobil","Mobile",7,[349,350,353,356,359],{"key":241,"name":242,"field":344},{"key":351,"name":352,"field":344},"ios-swift","iOS (Swift)",{"key":354,"name":355,"field":344},"android-kotlin","Android (Kotlin)",{"key":357,"name":358,"field":344},"flutter","Flutter",{"key":360,"name":361,"field":344},"react-native","React Native",{"key":363,"name_tr":364,"name_en":365,"sort":366,"specializations":367},"security","Güvenlik","Security",8,[368,369,372,375,378,381],{"key":241,"name":242,"field":363},{"key":370,"name":371,"field":363},"appsec","AppSec",{"key":373,"name":374,"field":363},"offensive-pentest","Offensive \u002F Pentest",{"key":376,"name":377,"field":363},"cloud-security","Cloud Security",{"key":379,"name":380,"field":363},"devsecops","DevSecOps",{"key":382,"name":383,"field":363},"blue-team-incident","Blue Team \u002F Incident",{"key":385,"name_tr":386,"name_en":387,"sort":388,"specializations":389},"qa-test-automation","QA \u002F Test Otomasyonu","QA \u002F Test Automation",9,[390],{"key":241,"name":242,"field":385},{"key":392,"name_tr":393,"name_en":393,"sort":394,"specializations":395},"data-engineer","Data Engineer",10,[396],{"key":241,"name":242,"field":392},{"key":398,"name_tr":399,"name_en":400,"sort":401,"specializations":402},"game-dev","Oyun Geliştirme","Game Development",11,[403],{"key":241,"name":242,"field":398},{"key":405,"name_tr":406,"name_en":406,"sort":407,"specializations":408},"ml-engineer","ML Engineer",12,[409],{"key":241,"name":242,"field":405},[14,15,16],{"junior":412,"mid":414,"senior":415},{"questions":413,"median_sec":3},20,{"questions":413,"median_sec":3},{"questions":413,"median_sec":3},[417,10],"tr",[419,420],"google","github",21750,true]