US phone number format.

mrchow19910319 · January 21, 2019

I am currently doing a freecodecamp algorithm challenge where I need to write a program to validate phone number.

https://learn.freecodecamp.org/javascript-algorithms-and-data-structures/javascript-algorithms-and-data-structures-projects/telephone-number-validator

I am doing this challenge right now, the thing I want to ask has nothing to do with logic or coding.
I am not from the US, could someone explain the US phone number format a little bit?

There are a few example that are given from the quest:

Quote

555-555-5555
(555)555-5555
(555) 555-5555
555 555 5555
5555555555
1 555 555 5555

So, my understanding is that there are a few requirements:

10 digit with numbers only

if the user added 1 in front of the 10 digit it counts too.

So, the thing I need to get rid of from the user inputs are non-number letter. What about 2 555 555 5555, is this a valid number??

PineyCreek · January 21, 2019

US's country code is 1. In example number XXX-YYY-ZZZZ, the X's are the area code, the Y's are the exchange number, and the Z's are the identifier. Within the US (and likewise with other countries) the country code is usually not necessary except with particular phone systems.

This:

555-555-5555
(555)555-5555
(555) 555-5555
555 555 5555
5555555555
1 555 555 5555

Is just for convenience/formatting. It might help someone remember a number better. The spaces mean nothing, and the 1 can be ignored as it is the country code. If dialing internationally you'll prefix the number with the country code, ex. Australia's country code is 61.