用typescript编译出来的代码，如下：

typescript:

function test(template, name, age) {
    console.log(template);
    console.log(name);
    console.log(age);
}
let myname: string = "Keyon";
let myage: number = 18;
test`Hello, my name is ${myname}, I'm ${myage}.`;

编译后的javascript:

function test(template, name, age) {
    console.log(template);
    console.log(name);
    console.log(age);
}
var myname = "Keyon";
var myage = 18;
(_a = ["Hello, my name is ", ", I'm ", "."], _a.raw = ["Hello, my name is ", ", I'm ", "."], test(_a, myname, myage));
var _a;

(_a = ["Hello, my name is ", ", I'm ", "."], _a.raw = ["Hello, my name is ", ", I'm ", "."], test(_a, myname, myage));这里直接一个小括号，里边的像参数一样的，是什么意思？还有那个 _a.raw 是什么？