Viewing github.com/facebook/react/fixtures/fiber-debugger/src/describeFibers.js

```
let nextFiberID = 1;
```
```
const fiberIDMap = new WeakMap();
```
```
function getFiberUniqueID(fiber) {
```
```
  if (!fiberIDMap.has(fiber)) {
```

    fiberIDMap.set(fiber, nextFiberID++);

```
  }
```
```
  return fiberIDMap.get(fiber);
```
```
}
```
```
function getFriendlyTag(tag) {
```
```
  switch (tag) {
```
```
    case 0:
```
```
      return '[indeterminate]';
```
```
    case 1:
```
```
      return '[fn]';
```
```
    case 2:
```
```
      return '[class]';
```
```
    case 3:
```
```
      return '[root]';
```
```
    case 4:
```
```
      return '[portal]';
```
```
    case 5:
```
```
      return '[host]';
```
```
    case 6:
```
```
      return '[text]';
```
```
    case 7:
```
```
      return '[coroutine]';
```
```
    case 8:
```
```
      return '[handler]';
```
```
    case 9:
```
```
      return '[yield]';
```
```
    case 10:
```
```
      return '[frag]';
```
```
    default:
```
```
      throw new Error('Unknown tag.');
```
```
  }
```
```
}
```
```
function getFriendlyEffect(flags) {
```
```
  const effects = {
```
```
    1: 'Performed Work',
```
```
    2: 'Placement',
```
```
    4: 'Update',
```
```
    8: 'Deletion',
```
```
    16: 'Content reset',
```
```
    32: 'Callback',
```
```
    64: 'Err',
```
```
    128: 'Ref',
```
```
  };
```
```
  return Object.keys(effects)
```
```
    .filter(flag => flag & flags)
```
```
    .map(flag => effects[flag])
```
```
    .join(' & ');
```
```
}
```

export default function describeFibers(rootFiber, workInProgress) {

```
  let descriptions = {};
```
```
  function acknowledgeFiber(fiber) {
```
```
    if (!fiber) {
```
```
      return null;
```
```
    }
```

    if (!fiber.return && fiber.tag !== 3) {

```
      return null;
```
```
    }
```

    const id = getFiberUniqueID(fiber);

```
    if (descriptions[id]) {
```
```
      return id;
```
```
    }
```
```
    descriptions[id] = {};
```
```
    Object.assign(descriptions[id], {
```
```
      ...fiber,
```
```
      id: id,
```
```
      tag: getFriendlyTag(fiber.tag),
```

      flags: getFriendlyEffect(fiber.flags),

      type: fiber.type && '<' + (fiber.type.name || fiber.type) + '>',

      stateNode: `[${typeof fiber.stateNode}]`,

      return: acknowledgeFiber(fiber.return),

      child: acknowledgeFiber(fiber.child),

      sibling: acknowledgeFiber(fiber.sibling),

      nextEffect: acknowledgeFiber(fiber.nextEffect),

      firstEffect: acknowledgeFiber(fiber.firstEffect),

      lastEffect: acknowledgeFiber(fiber.lastEffect),

      alternate: acknowledgeFiber(fiber.alternate),

```
    });
```
```
    return id;
```
```
  }
```

  const rootID = acknowledgeFiber(rootFiber);

  const workInProgressID = acknowledgeFiber(workInProgress);

```
  let currentIDs = new Set();
```
```
  function markAsCurrent(id) {
```
```
    currentIDs.add(id);
```
```
    const fiber = descriptions[id];
```
```
    if (fiber.sibling) {
```
```
      markAsCurrent(fiber.sibling);
```
```
    }
```
```
    if (fiber.child) {
```
```
      markAsCurrent(fiber.child);
```
```
    }
```
```
  }
```
```
  markAsCurrent(rootID);
```
```
  return {
```
```
    descriptions,
```
```
    rootID,
```

    currentIDs: Array.from(currentIDs),

```
    workInProgressID,
```
```
  };
```
```
}
```

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