FA-96578 / Phone number formatting / Member archive

As-you-type ten-digit formatter: a typed national prefix becomes part of the area code · case 03

"1555" renders as "(155) 5".

Member previewVariant 3 · 3 implementations · 11 checks per implementation

Case contract

Input the digits typed so far. A leading 1 becomes the prefix "1 ". With more than ten remaining digits the raw input is returned. Up to 3 digits are shown bare; 4..6 as "(AAA) E.."; 7..10 as "(AAA) EEE-S...". The result is stripped of surrounding spaces.

Why this case matters

Input masks re-render on every keystroke; premature punctuation or a lost prefix makes the caret jump and corrupts what users type.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
national prefix with three digits	`"(175) 5"`	`"1 755"`	Failed

MEMBER ARCHIVE

The complete case is available to members.

This record includes three runnable implementations, regression fixtures, execution results, and source hashes.

Member access is invitation-based. Sign in with your invited account to inspect the sources.