不要重复发明轮子。看看谷歌的LibPhonenumber，它有一个javascript实现，可以“按你输入”格式化。你可以试试demo here。
示例的输出：

****Parsing Result:****
{"country_code":1,"national_number":2345678900,"raw_input":"+12345678900 ","country_code_source":1}

****Validation Results:****
Result from isPossibleNumber(): true
Result from isValidNumber(): true
Result from isValidNumberForRegion(): false
Phone Number region: US
Result from getNumberType(): FIXED_LINE_OR_MOBILE

****Formatting Results:**** 
E164 format: +12345678900
Original format: +1 234-567-8900
National format: (234) 567-8900
International format: +1 234-567-8900
Out-of-country format from US: 1 (234) 567-8900
Out-of-country format from Switzerland: 00 1 234-567-8900
Format for mobile dialing (calling from US): +1 234-567-8900
Format for national dialing with preferred carrier code and empty fallback carrier code: (234) 567-8900

****AsYouTypeFormatter Results****
Char entered: + Output: +
Char entered: 1 Output: +1
Char entered: 2 Output: +1 2
Char entered: 3 Output: +1 23
Char entered: 4 Output: +1 234
Char entered: 5 Output: +1 234-5
Char entered: 6 Output: +1 234-56
Char entered: 7 Output: +1 234-567
Char entered: 8 Output: +1 234-567-8
Char entered: 9 Output: +1 234-567-89
Char entered: 0 Output: +1 234-567-890
Char entered: 0 Output: +1 234-567-8900
Char entered:   Output: +12345678900

这适用于所有（大多数？）国家，并确保您使用的格式是全球使用.如果我没有弄错，它是在Android手机中使用，最肯定的是在许多其他项目，我认为它可以被视为一个事实上的标准格式化数字.

你可以在replace方法中使用一个replacement函数。通过这个函数，你可以根据你所需要的条件来构建你的字符串：

function numberFormatter(number) {
  return number.replace(
    /^(\+\d{1})(\d{1,3})?(\d{1,3})?(\d{1,2})?(\d{1,2})?$/,
    (match, p1, p2, p3, p4, p5) => p1 + ' ' + (p2 ? '(' + p2 + (p2.length > 2 ? ')' : '') : '') + (p3 ? ' ' + p3 : '') + (p4 ? ' ' + p4 + (p4.length > 1 ? '-' : '') : '') + (p5 ? p5 : '')
  )
}

// Utils

// Tests which worked from your code
expect("+12345678900", "+1 (234) 567 89-00")
expect("+1234567890", "+1 (234) 567 89-0")
expect("+123456789", "+1 (234) 567 89-")
expect("+12345", "+1 (234) 5")

// Tests which work now
expect("+12345678", "+1 (234) 567 8")
expect("+1234567", "+1 (234) 567")
expect("+123", "+1 (23")

function expect(input, expectedResult) {
  const formattedNumber = numberFormatter(input)
  if (formattedNumber === expectedResult) {
    console.log(`PASSED: "${input}" -> "${expectedResult}"`);
  } else {
    console.error(`FAILED: "${input}" -> Expected: "${expectedResult}", Received: "${formattedNumber}"`);
  }
}

题外话：我对你的要求有点困惑。我认为替代品更有意义：

+1 (234) 567 89     -> +1 (234) 567 89  instead of +1 (234) 567 89-
+1 (23)             -> +1 (23)          instead of +1 (23