CHALLENGE / MEDIUM

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Mask Email Username

For an email containing one @, replace all but the first character of the username with *. Preserve domain and original case.

Input["ada@example.com"]Expected output"a**@example.com"

Input["x@y.io"]Expected output"x@y.io"

Mode: Function (automatic calls). Eight tests: two public and six hidden.

The test harness calls your function automatically. No stdin or console.log is required.

No execution requested.

Test 1: ["ada@example.com"] → "a**@example.com" Not run

Test 2: ["x@y.io"] → "x@y.io" Not run

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