Forgotten null checks and silent failures

TSjunior

Main had a minimal getUserSummary returning just the name. The PR extends it: age from birthDate and the first role. It works in the happy path — but you know prod isn't the happy path. Walk the diff and find every new crash point.

PR: lesson.typescript +7 −04 проблем

11 interface User {

22 id: string

33 firstName: string

44 lastName: string

5+ birthDate?: string

56 roles: string[]

67 }

78

89 export function getUserSummary(userId: string, users: User[]): string {

910 const user = users.find((u) => u.id === userId)

10- if (!user) return 'Unknown user'

11- return `${user.firstName} ${user.lastName}`

11+ const fullName = user.firstName + ' ' + user.lastName

12+

13+ const birthYear = parseInt(user.birthDate.split('-')[0], 10)

14+ const age = new Date().getFullYear() - birthYear

15+

16+ const role = user.roles[0].toUpperCase()

17+

18+ return `${fullName}, ${age}, ${role}`

1219 }

Шаг 1 из 6

Hunt for crash points

Strategy: walk each line and ask "what if this value is null / undefined / empty?". Prod is not the happy path. Anything that **can** be empty **will** be empty, sooner or later. Look at the code and note every place where something might come in empty.

ArchCase

ArchCase

Forgotten null checks and silent failures

Hunt for crash points