randomValue ='Mateo';console.log(randomValue.name);// Error: Object is of type unknownrandomValue();// Error: Object is of type unknownrandomValue.toUpperCase();// Error: Object is of type unknown 备注 any和unknown之间的核心区别在于你无法与unknown类型的变量进行交互;这样做会产生“编译器”错误。
functionadd(a:number,b:number):number;functionadd(a:string,b:string):string;functionadd(a:string,b:number):string;functionadd(a:number,b:string):string;functionadd(a:Combinable,b:Combinable){// type Combinable = string | number;if(typeofa==='string'||typeofb==='string'){returna.toStri...
你可以使用 juggle-check,它检查 null 和 undefined,或者使用 strict-check,它返回true设置为null的值,并且不会评估true未定义的变量。 代码语言:javascript 复制 //juggleif(x==null){}vara:number;varb:number=null;functioncheck(x,name){if(x==null){console.log(name+' == null');}if(x===null){c...
function printValue(value: string | number): void { if (typeof value === 'string') { console.log(`The value is a string: ${value}`); } else if (typeof value === 'number') { console.log(`The value is a number: ${value}`); } } class Person { name: string;constructor(name...
When checking if a union is assignable to some target type, we have to check if every member of the union is assignable to the target type, and that can be very slow. In TypeScript 5.3, we peek at the original intersection form that we were able to tuck away. When we compare the ...
Examples are (x: number) => number for functions and { x: number, y: number } for objects. If there is no certainty at all about the type, any is the right choice, not Object. If the only known fact about the type is that it's some object, use the type object, not Object ...
But that’s just the default. We can now easily run and debug tests without a full type-check from TypeScript if we really want. So transforming JavaScript and type-checking have been decoupled for us, and can run independently if we need. ...
uses theIceCreaminterface as parameter type. This function checks the number of scoops in the IceCream object and returns a message based on the result. To test your work, pass in the object{flavor: 'vanilla', scoops: 5}as a parameter and check the result by returning it to the cons...
interface ICustomerShort { Id: number; CalculateDiscount( discountAmount: ( discountClass: string, multipleDiscount: boolean ) => number): number } That parameter is defined using a function type that accepts two parameters (one of string, one of boolean) and returns a number. If you’re a...
相比于暴力的 any，使用 unknown 来转换类型的操作就比较中肯：「因为鹿和马都有共同的 unknown 的祖先...