Simply anything is not defined in JavaScript, is undefined, doesn't matter if it's a property inside an Object/Array or as just a simple variable... JavaScript ... ... <看更多>

JavaScript 的資料型態有七種-字串（string）、數字（number）、布林值（boolean）、null、undefined、物件（object）與symbol。 ... <看更多>

The undefined is a primitive type in JavaScript. So the undefined is a type. And the undefined type has exactly one value that is undefined . ... <看更多>

TypeScript Version: 3.7.0-dev.20190824 Search Terms: Object is possibly undefined TS2532 Code interface IData { data: number; } ... ... <看更多>