如何在打字稿類型中定義默認值

Question

在打字稿中定義自定義類型時我想說如果未定義內部元素，則將使用默認值。

因此，例如：

function custom(a:{required:string, optional='haha'}) { 

} 

這不工作:(

我不能使用type因爲這句法也不工作這將是很好的找到正確的語法使用。

Answer 1

打字稿支持這一點，我想代碼將最好的解釋：

//You can set defaults for variables 
var defaultingString: string = "Default" 

//You can create custom types through classes 
var myCustomType: TestClass; 
class TestClass { 
    //You can set defaults for variables in classes too 
    testVarA: string = "Default"; 

    //You can handle it in a class constructor 
    //(which can also have defaults in it's parameters) 
    testVarB: string; 
    constructor(public someParam: string = "DefaultParam") { 
     if (!this.testVarB){ 
      this.testVarB = someParam; 
     } 
    } 

    //Works in regular functions both for parameters and return type 
    testFoo (someOtherParam: string = this.testVarA): string { 
     return someOtherParam; 
    } 
} 

粘貼到https://www.typescriptlang.org/play/並玩弄:)