如何在打字稿类型中定义默认值

Question

在打字稿中定义自定义类型时我想说如果未定义内部元素，则将使用默认值。

因此，例如：

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

} 

这不工作:(

我不能使用type因为这句法也不工作这将是很好的找到正确的语法使用。

Answer 1

打字稿支持这一点，我想代码将最好的解释：

//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; 
    } 
} 

粘贴到https://www.typescriptlang.org/play/并玩弄:)