Typescript 3.9 新特性

1. Promise.all

Typescript 3.9 引入了 Promise.all 的类型定义。

const promise1 = Promise.resolve(3);
const promise2 = 42;
const promise3 = new Promise<string>((resolve, reject) => {
  setTimeout(resolve, 100, "foo");
});

// expected to be `Promise<[number, number, string]>`
const p = Promise.all([promise1, promise2, promise3] as const);

2. Short-Circuiting Assignment Operators

Typescript 3.9 引入了短路赋值运算符，可以在赋值时进行短路运算。

let x = 0;
x ||= 12;
console.log(x); // 12

let y = 0;
y &&= 12;
console.log(y); // 0