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reference) long after the program has no real use for them, so the GC has no way to know it can free them.",{"id":170,"topic":9,"difficulty":171,"body":172,"options":173,"correct_key":163,"explanation":182},"019f7517-0f31-70d8-948e-dec2ff271277",2,"Which of these best describes 'mark-and-sweep', the garbage collection strategy used by modern JS engines?",[174,176,178,180],{"key":157,"text":175},"Every object keeps a reference count that frees it at zero",{"key":160,"text":177},"Memory is defragmented by moving objects to the start of the heap",{"key":163,"text":179},"The engine marks everything reachable from root references, then sweeps what's unmarked",{"key":166,"text":181},"Objects that have simply existed longer than some fixed number of milliseconds get freed automatically by a background timer","Mark-and-sweep starts from GC roots, marks everything reachable by walking references, then frees whatever wasn't marked. This is why unreachable cycles are collected fine, unlike naive reference counting.",{"id":184,"topic":9,"difficulty":171,"body":185,"options":186,"correct_key":157,"explanation":195},"019f7517-0f33-74b6-9e66-5187d1e67cf7","```javascript\nfunction makeCycle() {\n  let a = {};\n  let b = {};\n  a.other = b;\n  b.other = a;\n  return \"done\";\n}\nmakeCycle();\n```\nAfter `makeCycle()` returns, are `a`, `b`, and the objects they point to eligible for garbage collection?",[187,189,191,193],{"key":157,"text":188},"Yes — nothing outside the function references them, so the unreachable cycle is collected",{"key":160,"text":190},"No — because `a` and `b` hold mutual references to each other, the engine can never determine that they're actually unreachable",{"key":163,"text":192},"Only `a` is collected; `b` survives because it was assigned second",{"key":166,"text":194},"Only if `delete a.other` is called first","Reference counting would get stuck on this cycle (count never hits zero), but mark-and-sweep doesn't care — once `makeCycle` returns, nothing reachable from the roots points to `a` or `b`, so both are collected together.",{"id":197,"topic":9,"difficulty":171,"body":198,"options":199,"correct_key":166,"explanation":208},"019f7517-0f34-704c-81ce-b4cfc04fcdc0","A single-page app starts a `setInterval` inside a component's 'mount' logic to poll for updates, but never calls `clearInterval` when the user navigates away. What is the most likely consequence?",[200,202,204,206],{"key":157,"text":201},"Nothing — setInterval callbacks are GC'd once the DOM node is removed",{"key":160,"text":203},"The browser tab crashes right away",{"key":163,"text":205},"The interval stops itself once its DOM node becomes unreachable",{"key":166,"text":207},"It keeps running — its closure stays alive for the page's lifetime, and repeated navigations pile this up","A running timer is itself a root-reachable reference held by the runtime, so its callback closure can't be collected until `clearInterval` is called. DOM removal alone doesn't stop it.",{"id":210,"topic":9,"difficulty":171,"body":211,"options":212,"correct_key":160,"explanation":221},"019f7517-0f35-7907-ac8b-7487f2396f3a","```javascript\nconst detached = [];\nfunction cacheRow(row) {\n  detached.push(row);\n  row.remove();\n}\n```\nIf `cacheRow` is called repeatedly with `\u003Ctr>` elements, what happens over time?",[213,215,217,219],{"key":157,"text":214},"Removed rows are collected as soon as `.remove()` runs, array or not",{"key":160,"text":216},"Each row stays in memory because `detached` still references it — a detached DOM tree leak",{"key":163,"text":218},"The browser auto-clears `detached` once a row leaves the document",{"key":166,"text":220},"`row.remove()` throws because the element is referenced elsewhere","`.remove()` only detaches an element from the visible document tree; it doesn't affect JS reachability. As long as `detached` holds a reference, the (now invisible) DOM subtree is retained.",{"id":223,"topic":9,"difficulty":224,"body":225,"options":226,"correct_key":157,"explanation":235},"019f7517-0f37-7399-9a2e-2c6caaf02a1f",3,"A widget's constructor creates a brand-new closure function each time and attaches it to `window` as a `resize` listener, but never removes it when the widget is destroyed. The app creates and destroys this widget 50 times during a session. What's the effect?",[227,229,231,233],{"key":157,"text":228},"50 closures pile up on `window`, each keeping its own widget instance alive",{"key":160,"text":230},"Only the newest listener survives; duplicates get replaced automatically",{"key":163,"text":232},"`addEventListener` deduplicates identical function references automatically",{"key":166,"text":234},"No memory impact, since `resize` fires only occasionally","Each call to `addEventListener` with a distinct closure adds a new listener; `window` (a root-reachable object) then holds a live reference to every one of them, keeping every widget instance's closure — and whatever it captured — alive.",{"fields":237,"seniorities":410,"interview_shapes":411,"locales":416,"oauth":418,"question_count":421,"coach_enabled":422,"jd_match_enabled":422},[238,263,271,287,311,324,343,362,384,391,397,404],{"key":239,"name_tr":240,"name_en":240,"sort":153,"specializations":241},"backend","Backend",[242,245,248,251,254,257,260],{"key":243,"name":244,"field":239},"general","Genel",{"key":246,"name":247,"field":239},"go","Go",{"key":249,"name":250,"field":239},"python","Python",{"key":252,"name":253,"field":239},"java","Java",{"key":255,"name":256,"field":239},"csharp","C#\u002F.NET",{"key":258,"name":259,"field":239},"nodejs","Node.js",{"key":261,"name":262,"field":239},"php","PHP",{"key":5,"name_tr":6,"name_en":6,"sort":171,"specializations":264},[265,266,267,268,269,270],{"key":243,"name":244,"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":272,"name_tr":273,"name_en":273,"sort":224,"specializations":274},"fullstack","Fullstack",[275,276,277,278,279,280,281,282,283,284,285,286],{"key":243,"name":244,"field":272},{"key":246,"name":247,"field":239},{"key":249,"name":250,"field":239},{"key":252,"name":253,"field":239},{"key":255,"name":256,"field":239},{"key":258,"name":259,"field":239},{"key":261,"name":262,"field":239},{"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 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