code: function getNextVal(searchVal, mapping) {
    let value
    if (isMap(mapping)) {
      for (let [key, val] of mapping.entries()) {
        if (deepEqual(key, searchVal)) {
          value = val
          break
        }
      }
    } else {
      value = (mapping.find(keyVal => deepEqual(keyVal[0], searchVal)) || [])[1]
    }
  
    if (typeof value === 'function') {
      return value()
    }
    return value
  }
docs: Returns value in mapping corresponding to matching searchVal key.