FA-96583 / Phone number formatting / Member archive

As-you-type ten-digit formatter: a lone prefix keeps its trailing space · case 03

Typing "1" shows "1 " and the caret jumps.

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
lone national prefix	`"1 "`	`"1"`	Failed

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