Regex Explainer

Lookahead for password rules

Stacked lookaheads let you require several things at once without dictating their order.

/^(?=.*[a-z])(?=.*[A-Z])(?=.*\d).{8,}$/

Match a whole string consisting of a position followed by zero or more of any character, then "a" to "z", then a position followed by zero or more of any character, then "A" to "Z", then a position followed by zero or more of any character, then a digit, then 8 or more of any character.

What to check

  • Note

    Anchors match string ends, not line ends

    Without the m flag, ^ and $ match only the very start and end of the input — not the start and end of each line. On multi-line input this is often not what was intended.

    Fix: Add the m flag if the pattern should apply per line.

Step by step

  1. ^

    Anchor to the start of the input.

  2. (?=.*[a-z])

    Match a position followed by zero or more of any character, then "a" to "z".

  3. (?=.*[A-Z])

    Match a position followed by zero or more of any character, then "A" to "Z".

  4. (?=.*\d)

    Match a position followed by zero or more of any character, then a digit.

  5. .{8,}

    Match 8 or more of any character.

  6. $

    Anchor to the end of the input.

Details

Capture groups
None
Flags
None set

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