1const telephoneCheck = str => {
2  const regExp = /^1?\s?(\(\d{3}\)|\d{3})(\s|-)?\d{3}(\s|-)?\d{4}$/gm
3  return regExp.test(str)
4}
5
6telephoneCheck("27576227382");
7
8			/*			Regular Expression Explanation Below !!! 			*/
9
10/*
11	Expression : /^1?\s?(\(\d{3}\)|\d{3})(\s|-)?\d{3}(\s|-)?\d{4}$/gm
12    
13    ^ asserts position at start of a line
14    1? matches the character 1 literally (case sensitive)
15    ? Quantifier — Matches between zero and one times, as many times as possible, giving back as needed (greedy)
16    \s? matches any whitespace character (equal to [\r\n\t\f\v \u00a0\u1680\u2000-\u200a\u2028\u2029\u202f\u205f\u3000\ufeff])
17    ? Quantifier — Matches between zero and one times, as many times as possible, giving back as needed (greedy)
18    1st Capturing Group (\(\d{3}\)|\d{3})
19    1st Alternative \(\d{3}\)
20    \( matches the character ( literally (case sensitive)
21    \d{3} matches a digit (equal to [0-9])
22    {3} Quantifier — Matches exactly 3 times
23    \) matches the character ) literally (case sensitive)
24    2nd Alternative \d{3}
25    \d{3} matches a digit (equal to [0-9])
26    {3} Quantifier — Matches exactly 3 times
27    2nd Capturing Group (\s|-)?
28    ? Quantifier — Matches between zero and one times, as many times as possible, giving back as needed (greedy)
29    1st Alternative \s
30    \s matches any whitespace character (equal to [\r\n\t\f\v \u00a0\u1680\u2000-\u200a\u2028\u2029\u202f\u205f\u3000\ufeff])
31    2nd Alternative -
32    - matches the character - literally (case sensitive)
33    \d{3} matches a digit (equal to [0-9])
34    {3} Quantifier — Matches exactly 3 times
35    3rd Capturing Group (\s|-)?
36    ? Quantifier — Matches between zero and one times, as many times as possible, giving back as needed (greedy)
37    1st Alternative \s
38    \s matches any whitespace character (equal to [\r\n\t\f\v \u00a0\u1680\u2000-\u200a\u2028\u2029\u202f\u205f\u3000\ufeff])
39    2nd Alternative -
40    \d{4} matches a digit (equal to [0-9])
41    {4} Quantifier — Matches exactly 4 times
42    $ asserts position at the end of a line
43    Global pattern flags
44    g modifier: global. All matches (don't return after first match)
45    m modifier: multi line. Causes ^ and $ to match the begin/end of each line (not only begin/end of string)
46*/
47
48// With love @kouqhar