Regular Expression to validate the Country code of mobile number in javascript

I need a regular expression that will test the input

1. Should start with only one + symbol or optional ( + should not come in between )
2. should not contain alphabets and any other special character
3. Should not contain consecutive + symbols

eg

• +91 (valid)
• 91 (valid)
• ++91 (invalid)
• +9+1 (invalid)
• 91+ (invalid)
• +91&*& (invalid)

Need your inputs on this . Thanks