TypeScript版本： 3.4.3
搜索词：

ServiceWorkerRegistration Update

代码

// A *self-contained* demonstration of the problem follows...
// Test this by running `tsc` on the command-line, rather than through another build tool such as Gulp, Webpack, etc.
let isUpdating: boolean;
navigator.serviceWorker.getRegistration().then(sw => {
    sw.update().then(result => {
        if (result.installing || result.waiting) {
            isUpdating = true;
        }
    });
});

预期行为：

result 是 ServiceWorkerRegistration 类型，并且 result.installing 和 result.waiting 是有效的。
https://developer.mozilla.org/en-US/docs/Web/API/ServiceWorkerRegistration/update

实际行为：

result 是 void 类型，tsc 报错
error TS2339: Property 'installing' does not exist on type 'void'.
error TS2339: Property 'waiting' does not exist on type 'void'.

Playground链接
相关问题：

#17590