JavaScript正则表达式验证姓氏：禁止全大写或全小写格式

Great question—your current regex handles valid characters but misses the casing constraint. Let's fix that while keeping support for edge cases like d'Arras or de Clemente.

Core Requirement Recap #

We need to:

• Allow letters (any case, mixed), spaces, commas, dots, apostrophes, and hyphens
• Block entries where all letters are uppercase (e.g., D'ARRAS, SMITH) or all letters are lowercase (e.g., de clemente, jones)

The Solution Regex #

Here's a refined regex that meets these needs:

^(?![^A-Z]+$)(?![^a-z]+$)[a-z ,.'-]+$

Or, if you prefer using the case-insensitive (i) modifier (which makes the character class more readable):

^(?![a-z ,.'-]+$)(?![A-Z ,.'-]+$)[a-z ,.'-]+$

How It Works #

Let's break down the key parts:

• ^ and $: Anchor the regex to match the entire string (no partial matches)
• (?![^A-Z]+$): Negative lookahead that ensures the string isn't entirely made of non-uppercase characters (i.e., there's at least one uppercase letter)
• (?![^a-z]+$): Negative lookahead that ensures the string isn't entirely made of non-lowercase characters (i.e., there's at least one lowercase letter)
• [a-z ,.'-]+: Matches all valid characters (letters, spaces, commas, dots, apostrophes, hyphens)

Test Cases #

Valid (Will Pass)

• d'Arras
• de Clemente
• O'Neil
• van der Sar
• De la Cruz

Invalid (Will Fail)

• D'ARRAS (all letters uppercase)
• de clemente (all letters lowercase)
• SMITH (all uppercase)
• jones (all lowercase)
• 123Smith (contains invalid numeric characters)

Notes #

• If your use case allows single-letter surnames (e.g., X or x), this regex will reject them (since they can't have mixed casing). If you need to support these, you'd need to add an exception—just let me know!
• The regex assumes symbols (spaces, commas, etc.) don't count toward casing checks, which aligns with standard surname formatting rules.

内容的提问来源于stack exchange，提问作者t99ver