在TypeScript中返回不同类型的数组

Question

In TypeScript 2.5.3 I've a bunch of selenium WebElements which are links. I need to get their targets in an array of strings. Caming from C# I would use Linq with .Select() which itself returns a list of the return type from the selector. In Typescript this doesn't seem to work so nicely:

    let categoryLinkElements = await this.driver.findElements(By.css('ul li a'));
    let categoryLinks = categoryLinkElements.filter(async linkElement => await linkElement.getAttribute('href'));

categoryLinkElements is an array of WebElement . And linkElement.getAttribute('href') returns Promise<string> . Cause await is used, I would expect that categoryLinks is an array of strings, like the same behavior of List.Select() in C#. Instead, categoryLinks is WebElement[] .

Why? And how can I get the correct return value?

Answer 1

Array.filter seems wrong here, instead it should be used to return the same value than the input array, but with some filter condition. Instead Array.map is the correct equivalent of List.Select in C#.

The following works as expected:

let categoryLinks = categoryLinkElements.map(async linkElement => await linkElement.getAttribute('href'));

As a beginner of Typescript and Javascript, this seems a stupid question afterwards... sorry :/