@observablehq/inspector/src/immutable.js

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const SYMBOLS = [
  { symbol: "@@__IMMUTABLE_INDEXED__@@", name: "Indexed", modifier: true },
  { symbol: "@@__IMMUTABLE_KEYED__@@", name: "Keyed", modifier: true },
  { symbol: "@@__IMMUTABLE_LIST__@@", name: "List", arrayish: true },
  { symbol: "@@__IMMUTABLE_MAP__@@", name: "Map" },
  {
    symbol: "@@__IMMUTABLE_ORDERED__@@",
    name: "Ordered",
    modifier: true,
    prefix: true
  },
  { symbol: "@@__IMMUTABLE_RECORD__@@", name: "Record" },
  {
    symbol: "@@__IMMUTABLE_SET__@@",
    name: "Set",
    arrayish: true,
    setish: true
  },
  { symbol: "@@__IMMUTABLE_STACK__@@", name: "Stack", arrayish: true }
];

export function immutableName(obj) {
  try {
    let symbols = SYMBOLS.filter(({ symbol }) => obj[symbol] === true);
    if (!symbols.length) return;

    const name = symbols.find(s => !s.modifier);
    const prefix =
      name.name === "Map" && symbols.find(s => s.modifier && s.prefix);

    const arrayish = symbols.some(s => s.arrayish);
    const setish = symbols.some(s => s.setish);

    return {
      name: `${prefix ? prefix.name : ""}${name.name}`,
      symbols,
      arrayish: arrayish && !setish,
      setish
    };
  } catch (e) {
    return null;
  }
}