Flatten object

OSCC · JavaScript, Object, Recursion · Oct 19, 2020

Flattens an object with the paths for keys.

  • Use recursion.
  • Use Object.keys() combined with Array.prototype.reduce() to convert every leaf node to a flattened path node.
  • If the value of a key is an object, the function calls itself with the appropriate prefix to create the path using Object.assign().
  • Otherwise, it adds the appropriate prefixed key-value pair to the accumulator object.
  • You should always omit the second argument, prefix, unless you want every key to have a prefix.
const flattenObject = (obj, prefix = '') =>
  Object.keys(obj).reduce((acc, k) => {
    const pre = prefix.length ? `${prefix}.` : '';
    if (
      typeof obj[k] === 'object' &&
      obj[k] !== null &&
      Object.keys(obj[k]).length > 0
    )
      Object.assign(acc, flattenObject(obj[k], pre + k));
    else acc[pre + k] = obj[k];
    return acc;
  }, {});
flattenObject({ a: { b: { c: 1 } }, d: 1 }); // { 'a.b.c': 1, d: 1 }

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