Regex Password Validation

Description

You need to write regex that will validate a password to make sure it meets the following criteria:
At least six characters long
contains a lowercase letter
contains an uppercase letter
contains a number
Valid passwords will only be alphanumeric characters.

My answer

function validate(password) {
  return /^(?=.*\d)(?=.*[a-z])(?=.*[A-Z])[a-zA-Z0-9]{6,}$/.test(password);
}

Other solutions

function validate(password) {
  return  /^[A-Za-z0-9]{6,}$/.test(password) &&
          /[A-Z]+/           .test(password) &&
          /[a-z]+/           .test(password) &&
          /[0-9]+/           .test(password) ;
}

Wrap up

Regular expression - Assertions

Type

Boundary-type assertions

1. ^
   Matches the beginning of input. /^A/ does not match the "A" in "an A", but does match the first "A" in "An A".
2. $Matches the end of input. For example, /t$/ does not match the "t" in "eater", but does match it in "eat".
3. \b
   Matches a word boundary. Examples:
   /\bm/ matches the "m" in "moon".
   /oo\b/ does not match the "oo" in "moon", because "oo" is followed by "n" which is a word character.
   /oon\b/ matches the "oon" in "moon", because "oon" is the end of the string, thus not followed by a word character.
   /\w\b\w/ will never match anything, because a word character can never be followed by both a non-word and a word character.
4. \B
   Matches a non-word boundary. For example, /\Bon/ matches "on" in "at noon", and /ye\B/ matches "ye" in "possibly yesterday".

Other assertions

1. x(?=y): Lookahead assertion
   Matches "x" only if "x" is followed by "y". For example, /Jack(?=Sprat)/ matches "Jack" only if it is followed by "Sprat".
   /Jack(?=Sprat|Frost)/ matches "Jack" only if it is followed by "Sprat" or "Frost". However, neither "Sprat" nor "Frost" is part of the match results.
2. x(?!y): Negative lookahead assertion
   Matches "x" only if "x" is not followed by "y". For example, /\d+(?!.)/ matches a number only if it is not followed by a decimal point. /\d+(?!.)/.exec('3.141') matches "141" but not "3.
3. (?<=y)x: Lookbehind assertion
   Matches "x" only if "x" is preceded by "y". For example, /(?<=Jack)Sprat/ matches "Sprat" only if it is preceded by "Jack". /(?<=Jack|Tom)Sprat/ matches "Sprat" only if it is preceded by "Jack" or "Tom". However, neither "Jack" nor "Tom" is part of the match results.
4. (?<!y)x: Negative lookbehind assertion
   Matches "x" only if "x" is not preceded by "y". For example, /(?<!-)\d+/ matches a number only if it is not preceded by a minus sign. /(?<!-)\d+/.exec('3') matches "3". /(?<!-)\d+/.exec('-3') match is not found because the number is preceded by the minus sign.
   source: mdn web docs