Deeply traverse an object to replace or redact values using a regex and replacer function

deep-assign.js

export const assignDeep = (input, regex, replacer) => {
  const json = JSON.stringify(input)

  return JSON.parse(json, (k, v) =>
    typeof v === "string" && regex.test(k) ? replacer(v) : v
  )
}

export const redactDeep = (input, regex) =>
  assignDeep(input, regex, () => "[REDACTED]")

export const redactEllipsisDeep = (input, regex, minLength = 15) =>
  assignDeep(input, regex, (val) => {
    if (val.length <= minLength) {
      return "..."
    }

    const start = val.slice(0, 3)
    const end = val.slice(val.length - 3, val.length)

    return `${start}...${end}`
  })


const obj = {
  x: 1,
  y: 2,
  api_key: "hideme",
  f: (arg) => ({ x: 1}),
  a: [{
    z: 1,
    accessToken: "23u42u3i4kj3k4j2l3kj4",
    refreshToken: "4n53l4kj5kj4lk5j3lk4j5l3k4j5lk3j4",
  }],
  superSecret: "secret",
}

const result = assign(obj, /key|secret|token/i, (val) => "[REDACTED]")

/*
{ x: 1, 
  y: 2, 
  api_key: '[REDACTED]', 
  a: [ { z: 1, accessToken: '[REDACTED]', refreshToken: '[REDACTED]' } ], 
  superSecret: '[REDACTED]' }
*/

Useful for redacting secrets, api keys and tokens during logging.