如果一個類型是多個類型的聯(lián)合類型，且多個類型含有一個公共屬性，那么就可以利用這個公共屬性，來創(chuàng)建不同的類型保護(hù)區(qū)塊。

enum CarTransmission {Automatic = 200,Manual = 300 }interface Motorcycle {vType: "motorcycle"; // discriminantmake: number; // year }interface Car {vType: "car"; // discriminanttransmission: CarTransmission }interface Truck {vType: "truck"; // discriminantcapacity: number; // in tons }

基于前面定義了三個接口，我們可以創(chuàng)建一個?Vehicle?聯(lián)合類型：

type Vehicle = Motorcycle | Car | Truck;

接下來進(jìn)行類型守衛(wèi)

function evaluatePrice(vehicle: Vehicle) {switch(vehicle.vType) {case "car":return vehicle.transmission * EVALUATION_FACTOR;case "truck":return vehicle.capacity * EVALUATION_FACTOR;case "motorcycle":return vehicle.make * EVALUATION_FACTOR;} }

完整demo

interface car{type:'car',age:number } interface bicycle{type:'bicycle',sex: number } interface boat{type:'boat',grade:number }type Vehicle = car | bicycle | boat; const EVALUATION_FACTOR = Math.PI; function evaluatePrice(vehicle: Vehicle) {switch(vehicle.type) {case "car":return vehicle.age * EVALUATION_FACTOR;case "bicycle":return vehicle.sex * EVALUATION_FACTOR;case "boat":return vehicle.grade * EVALUATION_FACTOR;} }const myTruck: car = { type: "car", age: 9.5 }; const VehicleDate = evaluatePrice(myTruck); console.log(VehicleDate);

總結(jié)

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