如何在typescript类型中定义默认值

时间:2016-08-18 10:43:59

标签: typescript typescript1.8

在Typescript中定义自定义类型时,我想说如果没有定义内部元素,那么将使用默认值。

所以例如:

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

}

这不起作用:(

我无法使用type,因为该语法也不起作用。找到要使用的正确语法会很高兴。

1 个答案:

答案 0 :(得分:-1)

TypeScript支持这一点,我认为代码最能解释它:

//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/并玩游戏:)