They look useful from a specific mindset. How about these?

    function map_unless_nested(arr, cb){
      var res = []
      var has_nested = arr.some(function(item){ 
        if (item instanceof Array) return true
        res.push(cb(item))
      })
      return has_nested ? [] : res
    }

    function map_first_innermost(arr, cb){
      var res = []
      var has_nested = arr.some(function(item){ 
        if (item instanceof Array) return true
        res.push(cb(item))
      })
      return has_nested
        ? map_first_innermost(res[res.length-1], cb)
        : res
    }