Two positive lookaheads

JavaScript
#1

hi I am new here this is my first ever post on i been searching for this problem but i didn’t find it anywhere in this challenge i only want to know what is the meaning of
two parenthesis (?=)(?=) i know both are positive lookaheads but can someone explain to me what if i write this regex (?=\w{3,6})(?=\d) isn’t that mean that lookahead for aleast 3 to 6 char’s and 1 digit. but when my string = “aaa1”; that is false .

i just want to know what is the meaning to these two lookaheads

please thank you.

#2

Regex traverses string with the cursor, just like you would do in text editor. Let’s examine string 'aaa1' with cursor (|):

/** Position 0 */
|aaa1
// Look ahead for 3-6 alphanumeric characters: CHECK
// Look ahead for digit: FAIL (it is "a" ahead)

/** Position 1 */
a|aa1
// Look ahead for 3-6 alphanumeric characters: CHECK
// Look ahead for digit: FAIL (it is "a" ahead)

/** Position 2 */
aa|a1
// Look ahead for 3-6 alphanumeric characters: FAIL
// Look ahead for digit: FAIL (it is "a" ahead)

/** Position 3 */
aaa|1
// Look ahead for 3-6 alphanumeric characters: FAIL
// Look ahead for digit: CHECK

As you can see there is no such case where both lookaheads are successful. Hopefully this will help :slight_smile:

1 Like
#3

Sir, Thank you very much .I been looking this kind of explanation now i understand both lookaheads are being checked at the same position.Sometimes it is impossible to have a
alphabet and number is the same position that was my confusion for last two days.

now i understand that:

let str = “abc123”;
let regex = /(?=\w{3,6})(?=\d)/;
console.log(str.match(regex)) // [ ‘’, index: 3, input: ‘abc123’, groups: undefined ]

it is matching in position or index 3 because there are 3 char’s and digit.

thank’s again .

#4