regex match no value code example

Example 1: regex match any number

For matching an integer number of one single char/digit, specify:
[0-9]
But for matching any number of more than one char/digit; add "+":
[0-9]+
Example for matching hour with minutes of HH:MM format in a file:
grep "[0-9]\+\:[0-9]\+" file.txt

Example 2: regex not something

// You can use (?!...) like the example below

let names = ['JOAO', 'JOHN', 'JOANA', 'JOABE'];
for(let n of names)
{
  	/(JO)(?!A)/.test(n);
	// only true on 'JOHN'
}