TypeScript implementation of extracting every leaf values of given object into array

deepValues.ts

/**
 * @param obj anything
 * @param isSafe whether protect mutual dependency cycle case
 * @returns every primitive properties of nested objects or arrays
 */
function deepValues(obj: any, isSafe: boolean = false): any[] {
  const out = [] as any[]
  const dup = [] as (any[] | object)[]

  function traverse(current: any) {
    if (current == null || ['number', 'string', 'boolean', 'function'].includes(typeof current)) {
      out.push(current)
      return out
    }

    if (isSafe && dup.indexOf(current) > -1) {
      return out
    }
    dup.push(current)

    if (current instanceof Array) {
      current.forEach(traverse)
      return out
    }
    
    Object.values(current).forEach(traverse)
    return out
  }

  return traverse(obj)
}

Note that when isSafe === true, time complexity blows up to O(n^2) where n is the number of non primitive things. There is no way to identify any arbitrary object nor array efficiently.