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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Conversions/RgbHslConversion: rgbToHsl mutates (and returns) its input array instead of a copy","articleBody":"**Description**\n\n`Conversions/RgbHslConversion.js::rgbToHsl` mutates its input array. It aliases the argument with `let colorHsl = colorRgb` (no copy) and then overwrites `colorHsl[0..2]` in place, so the caller's RGB array is destroyed and replaced with the HSL result.\n\n```js\nconst rgbToHsl = (colorRgb) =\u003e {\n  ...\n  let colorHsl = colorRgb        // \u003c- alias, NOT a copy\n  ...\n  colorHsl[0] = red / limit      // mutates caller's array\n  ...\n  colorHsl[0] = Math.round(hue)  // final HSL written back into the input array\n  colorHsl[1] = Math.round(saturation * 100)\n  colorHsl[2] = Math.round(luminance * 100)\n  return colorHsl\n}\n```\n\nThe returned value is the *same array object* as the input, so a caller that still needs its RGB values loses them.\n\n**To Reproduce** (verified with Node):\n\n```js\nconst input = [24, 98, 118]\nconst result = rgbToHsl(input)\n// result            -\u003e [193, 66, 28]   (correct HSL)\n// input             -\u003e [193, 66, 28]   \u003c- the caller's RGB array was overwritten\n// input === result  -\u003e true            \u003c- same object, not a copy\n```\n\n**Expected behavior**\n\n`rgbToHsl` returns a new HSL array and leaves the input RGB array unchanged (a conversion function should not have side effects on its argument).\n\n**Actual behavior**\n\nThe input array is mutated in place and is returned as the result (`input === result`), so the original RGB data is destroyed.\n\n**Suggested fix**\n\nWork on a copy instead of aliasing the input:\n\n```js\nlet colorHsl = [...colorRgb]\n```\n\nThe HSL math itself is correct; only the in-place mutation of the argument needs fixing.\n","author":{"url":"https://github.com/aimasteracc","@type":"Person","name":"aimasteracc"},"datePublished":"2026-06-18T02:21:21.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/1907/JavaScript/issues/1907"}