主要代码: interface Example { children?: Example[] } const example: Example = { children: [{ children: [] }] } if (example.children) { for (let i = 0; i < example.children.length; i++) { if (example.children[i] && example.children[i].children) { console.log(example.children[...
varvariableOne:any;varvariableTwo:any=null;functiontypeCheck(x:any, name:any){if(x==null) {console.log(name+' == null');}if(x===null) {console.log(name+' === null');}if(typeofx==='undefined') {console.log(name+' is undefined');}}typeCheck(variableOne,'variableOne');typeCh...
Local Variables: variable === undefined Properties: object.prop === undefined 但是:For undeclared variables, typeof foo will return the string literal “undefined”, whereas the identity check foo === undefined would trigger the error “foo is not defined”. 因此最好使用typeof来检测。 typeof...
AI代码解释 //juggleif(x==null){}vara:number;varb:number=null;functioncheck(x,name){if(x==null){console.log(name+' == null');}if(x===null){console.log(name+' === null');}if(typeofx==='undefined'){console.log(name+' is undefined');}}check(a,'a');check(b,'b'); 13...
number = null; function check(x, name) { if (x == null) { console.log(name + ' == null'); } if (x === null) { console.log(name + ' === null'); } if (typeof x === 'undefined') { console.log(name + ' is undefined'); } } check(a, 'a'); check(b, 'b');...
vara:number;varb:number=null;functioncheck(x, name){if(x ==null) {console.log(name +' == null');}if(x ===null) {console.log(name +' === null');}if(typeofx ==='undefined') {console.log(name +' is undefined');}}check(a,'a');chec...
TypeScript 里,undefined和null两者有各自的类型分别为undefined和null。 默认情况下null和undefined是所有类型的子类型。 就是说你可以把null和undefined赋值给number类型的变量。然而,如果你指定了--strictNullChecks标记,null和undefined只能赋值给void和它们各自的类型。
Type '[string, number, string]' is not assignable to type '[string, number]'. */ Any (任意值) any与类型系统中的任何类型都兼容。意味着可以将任何内容赋值给它,也可以将它赋值给任何类型。它能让你避开类型检查。 let variable: any = 'a string'; ...
Also, we can use==to performundefinedchecks in TypeScript. When==is used in the strict-check method, it will only check the type of the value, unlike the===operator. The==operator can do anullcheck using the strict-check method. It will returntrueif a variable isnullor even when it...
That meant that if a let or const-declared variable was accessed before it was initialized, we wouldn’t get an error. Instead, its value would just be observed as undefined. There had been instances where this difference meant that TypeScript’s downlevel-emit wasn’t behaving as per the ...