# Data flow — trekhleb/javascript-algorithms

> Canonical page: https://codevetter.com/unpack/javascript-algorithms/data-flow

# Data flow — trekhleb/javascript-algorithms

Scanned commit 85293e3e2b88f4d2ce330d956b139cf628aa1e82 (2026-07-25). Generated by codevetter codevetter 1.12.0 on 2026-09-22.

Data flow is simple and uniform: callers (tests or the playground) invoke a module's default export with plain JS values; the module mutates or returns in-memory structures; results are compared with Jest matchers. There is no persistence, network, or external state — the only file IO is the seam-carving test streaming PNG fixtures through pngjs. The Comparator-injection pattern and traversal callbacks are the two mechanisms that let callers steer internal behavior without subclassing.
- Inputs are plain JS values passed directly to functions/classes (e.g., factorial(number), quickSort.sort(array), linkedList.append(value)); there is no request/response, CLI parsing, or stdin handling anywhere in src/. — [src/algorithms/math/factorial/factorial.js#L5-13](https://github.com/trekhleb/javascript-algorithms/blob/85293e3e2b88f4d2ce330d956b139cf628aa1e82/src/algorithms/math/factorial/factorial.js#L5-L13) [src/data-structures/linked-list/LinkedList.js#L39-55](https://github.com/trekhleb/javascript-algorithms/blob/85293e3e2b88f4d2ce330d956b139cf628aa1e82/src/data-structures/linked-list/LinkedList.js#L39-L55)
- Comparator is the primary data-normalization seam: constructors accept an optional compareFunction, and all ordering decisions flow through comparator.equal/lessThan/greaterThan rather than native operators. — [src/utils/comparator/Comparator.js#L7-53](https://github.com/trekhleb/javascript-algorithms/blob/85293e3e2b88f4d2ce330d956b139cf628aa1e82/src/utils/comparator/Comparator.js#L7-L53) [src/algorithms/sorting/quick-sort/QuickSort.js#L32-37](https://github.com/trekhleb/javascript-algorithms/blob/85293e3e2b88f4d2ce330d956b139cf628aa1e82/src/algorithms/sorting/quick-sort/QuickSort.js#L32-L37) [src/data-structures/linked-list/LinkedList.js#L104-124](https://github.com/trekhleb/javascript-algorithms/blob/85293e3e2b88f4d2ce330d956b139cf628aa1e82/src/data-structures/linked-list/LinkedList.js#L104-L124)
- Sorting transforms input -> cloned array -> pivot-partitioned left/center/right arrays -> recursively sorted concatenated output; QuickSort clones the input (`[...originalArray]`) so the caller's array is never mutated. — [src/algorithms/sorting/quick-sort/QuickSort.js#L8-47](https://github.com/trekhleb/javascript-algorithms/blob/85293e3e2b88f4d2ce330d956b139cf628aa1e82/src/algorithms/sorting/quick-sort/QuickSort.js#L8-L47)
- Traversal algorithms move data through a callback pipeline: initCallbacks builds a closed-over `seen` map for allowTraversal, then each vertex flows enterVertex -> neighbor iteration gated by allowTraversal -> leaveVertex. — [src/algorithms/graph/breadth-first-search/breadthFirstSearch.js#L19-74](https://github.com/trekhleb/javascript-algorithms/blob/85293e3e2b88f4d2ce330d956b139cf628aa1e82/src/algorithms/graph/breadth-first-search/breadthFirstSearch.js#L19-L74) [src/algorithms/graph/depth-first-search/depthFirstSearch.js#L17-58](https://github.com/trekhleb/javascript-algorithms/blob/85293e3e2b88f4d2ce330d956b139cf628aa1e82/src/algorithms/graph/depth-first-search/depthFirstSearch.js#L17-L58)
- Queue is a thin adapter over LinkedList: enqueue delegates to append (tail), dequeue delegates to deleteHead (front), isEmpty checks linkedList.head — showing how data-structures compose as building blocks. — [src/data-structures/queue/Queue.js#L3-48](https://github.com/trekhleb/javascript-algorithms/blob/85293e3e2b88f4d2ce330d956b139cf628aa1e82/src/data-structures/queue/Queue.js#L3-L48) [src/data-structures/linked-list/LinkedList.js#L195-210](https://github.com/trekhleb/javascript-algorithms/blob/85293e3e2b88f4d2ce330d956b139cf628aa1e82/src/data-structures/linked-list/LinkedList.js#L195-L210)
- HashTable.set flows key -> hash() (char-code sum mod bucket count) -> buckets[hash] LinkedList -> find by callback -> append or update node.value.value; get/delete follow the same path. — [src/data-structures/hash-table/HashTable.js#L27-91](https://github.com/trekhleb/javascript-algorithms/blob/85293e3e2b88f4d2ce330d956b139cf628aa1e82/src/data-structures/hash-table/HashTable.js#L27-L91)
- Seam carving is the only flow touching the filesystem, and only in tests: pngLoad streams a .png via fs.createReadStream into pngjs, converts to an ImageData-shaped object, then resizeImageWidth mutates img.data in place while tracking a separate logical {w,h} size. — [src/algorithms/image-processing/seam-carving/__tests__/resizeImageWidth.node.js#L43-68](https://github.com/trekhleb/javascript-algorithms/blob/85293e3e2b88f4d2ce330d956b139cf628aa1e82/src/algorithms/image-processing/seam-carving/__tests__/resizeImageWidth.node.js#L43-L68) [src/algorithms/image-processing/seam-carving/resizeImageWidth.js#L217-251](https://github.com/trekhleb/javascript-algorithms/blob/85293e3e2b88f4d2ce330d956b139cf628aa1e82/src/algorithms/image-processing/seam-carving/resizeImageWidth.js#L217-L251)
- State owners are instance fields on the structures: LinkedList.head/tail, Graph.vertices/edges (plain objects keyed by getKey()), HashTable.buckets/keys, Heap.heapContainer array, LRUCache.nodesMap/size plus sentinel nodes. — [src/data-structures/linked-list/LinkedList.js#L8-16](https://github.com/trekhleb/javascript-algorithms/blob/85293e3e2b88f4d2ce330d956b139cf628aa1e82/src/data-structures/linked-list/LinkedList.js#L8-L16) [src/data-structures/graph/Graph.js#L5-9](https://github.com/trekhleb/javascript-algorithms/blob/85293e3e2b88f4d2ce330d956b139cf628aa1e82/src/data-structures/graph/Graph.js#L5-L9) [src/data-structures/hash-table/HashTable.js#L13-19](https://github.com/trekhleb/javascript-algorithms/blob/85293e3e2b88f4d2ce330d956b139cf628aa1e82/src/data-structures/hash-table/HashTable.js#L13-L19) [src/data-structures/heap/Heap.js#L16-18](https://github.com/trekhleb/javascript-algorithms/blob/85293e3e2b88f4d2ce330d956b139cf628aa1e82/src/data-structures/heap/Heap.js#L16-L18) [src/data-structures/lru-cache/LRUCache.js#L36-42](https://github.com/trekhleb/javascript-algorithms/blob/85293e3e2b88f4d2ce330d956b139cf628aa1e82/src/data-structures/lru-cache/LRUCache.js#L36-L42)
- Outputs are returned values (sorted arrays, found nodes, traversal orders accumulated by caller-supplied callbacks) plus toString() representations that tests use as the primary assertion mechanism (e.g., expect(linkedList.toString()).toBe('1,2')). — [src/data-structures/linked-list/LinkedList.js#L241-243](https://github.com/trekhleb/javascript-algorithms/blob/85293e3e2b88f4d2ce330d956b139cf628aa1e82/src/data-structures/linked-list/LinkedList.js#L241-L243) [src/data-structures/linked-list/__test__/LinkedList.test.js#L18-33](https://github.com/trekhleb/javascript-algorithms/blob/85293e3e2b88f4d2ce330d956b139cf628aa1e82/src/data-structures/linked-list/__test__/LinkedList.test.js#L18-L33)
- Graph.getAdjacencyMatrix materializes a derived NxN weight matrix filled with Infinity for non-edges by iterating vertices and their neighbors — an explicit transform from adjacency-list storage to matrix output for algorithms like floyd-warshall. — [src/data-structures/graph/Graph.js#L169-200](https://github.com/trekhleb/javascript-algorithms/blob/85293e3e2b88f4d2ce330d956b139cf628aa1e82/src/data-structures/graph/Graph.js#L169-L200)

Every claim links to its cited files at the pinned commit. Citations identify source evidence; they do not establish runtime correctness. Independent CodeVetter scan — not reviewed by upstream maintainers.

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