30秒学会 JavaScript 片段 – transform

Applies a function against an accumulator and each key in the object (from left to right).

Use Object.keys(obj) to iterate over each key in the object, Array.prototype.reduce() to call the apply the specified function against the given accumulator.

代码片段

const transform = (obj, fn, acc) => Object.keys(obj).reduce((a, k) => fn(a, obj[k], k, obj), acc);

使用样例

transform(
  { a: 1, b: 2, c: 1 },
  (r, v, k) => {
    (r[v] || (r[v] = [])).push(k);
    return r;
  },
  {}
); // { '1': ['a', 'c'], '2': ['b'] }