TypeScript里的混合类型

TypeScript的对象可以同时做为函数和对象使用，并带有额外的属性。

interface Counter {
    (start: number): string;
    interval: number;
    reset(): void;
}

function getCounter(): Counter {
    let counter = <Counter>function (start: number) { };
    counter.interval = 123;
    counter.reset = function () { };
    return counter;
}

let c = getCounter();
c(10);
c.reset();
c.interval = 5.0;

对应生成的JavaScript代码：

function getCounter() {
    var counter = function (start) { };
    counter.interval = 123;
    counter.reset = function () { };
    return counter;
}
var c = getCounter();
c(10);
c.reset();
c.interval = 5.0;