JSON Completer (closeJSON)

closeJSON.ts

/**
 * Given an incomplete JSON string, return the string with the missing
 * closing characters.
 * @param str - An incomplete json string
 */
export function closeJSON(incompleteJson: string) {
  let char = ''
  let lastChar = ''
  let chars = [...incompleteJson]
  let isQuoted = false
  let depthMap: Array<'{' | '['> = []

  for (let i = 0; i < chars.length; i++) {
    lastChar = char
    char = chars[i]
    if (isQuoted && char === '"' && lastChar !== '\\') {
      isQuoted = false
    } else if (!isQuoted) {
      switch (char) {
        case '"':
          if (lastChar !== '\\') {
            isQuoted = true
          }
          break
        case '{':
        case '[':
          depthMap.push(char)
          break
        case '}':
        case ']':
          depthMap.pop()
          break
      }
    }
  }
  if (isQuoted) {
    incompleteJson += '"'
  }
  while (depthMap.length > 0) {
    const toClose = depthMap.pop()
    if (toClose === '{') incompleteJson += '}'
    if (toClose === '[') incompleteJson += ']'
  }
  return incompleteJson
}