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[TypeScript] tsc Error Troubleshooting

本篇雜記收錄開發過程中 tsc error 及問題排除...

TS2304: Cannot find name 'process'​

error TS2304: Cannot find name 'process'

You need to make sure that the type definitions for Node are available. The way to do this depends on which version of TypeScript you are using.

$ npm install --save-dev @types/node

Ref: javascript - Read arguments from command line - error TS2304: Cannot find name 'process' - Stack Overflow

TS2345: Type 'T1' is not assignable to type 'T2'​

null​

Ref: Solve - Type 'null' is not assignable to type in TypeScript | bobbyhadz

TS2531: Object is possibly 'null'​

error TS2531: Object is possibly 'null'.

ts 在編譯時診斷到物件可能會爲 null, 所以給出了這樣一個提示: 對象可能爲 null.

雖可修改 tsconfig.json 中 strictNullChecks = false 讓編譯器不檢查 null, 但專案管理上還是應該嚴謹一些看待.

files is defined to be FileList | null so it can be null. You should either check for null (using an if) or use a "Non-null assertion operator" (!) if you are sure it is not null:

如果程式流程中, 物件可能為 null 的話, 應該要在讀取物件值之前, 先判斷是否為 null.

若程式流程可以確定物件不會是 null 的話, 解決方式是在物件之後加一個 ! . 驚嘆號在 ts 編譯器中, 是物件 not null 的斷言操作符, 編譯器看到這個符號, 不會在編譯時檢查是否為 null.

! 只是告訴編譯器在編譯不要檢查是否可能為 null, 開發時要確認流程上不會造成 null 才可使用, 否則實際執行還是會出錯.

Ref: angular - TS2531: Object is possibly 'null' - Stack Overflow