https://github.com/smallinsect/MyJS/blob/main/TypeScript/define.ts 1 // a是undefined表示变量未定义，理解为变量不存在。2 // a=null表示变量值为空值，理解为变量存在但没有值。3 4 // 变量a旁边的问号?，表示该字段可有可无5 // 如果变量a没有赋值，这个字段不存在6 // 如果变量a赋值，则这个字段存在7 8 // 变量a旁边没有问号，该字段必须赋值，不赋值，则报错该字段必须赋值。9 10 // 动物 11 interface IAnimal { 12 ...
In this lesson, were going to look at how to perform null checks with assertion functions. Were going to assert that a nullable value doesnt hold the value null. In the process, were going to learn how assertion functions integrate with TypeScripts control flow analysis.const root = document.getElementById("root") `root` can be `HTMLElement` or `null` type.root.addEventListener("click", () => {})I...