如何检查documentElement中的项目，“输入”无效

Question

In JavaScript I have this test 'ontouchstart' in document.documentElement . If the event exists (even if null) it evaluates to true otherwise to false . I don't know how to do the equivalent in CoffeeScript. Writing it exactly as is translates to using an __indexOf function which does not do the same thing (it is always returning false).

You can also try 'onmousemove' for an event that always exists.

Answer 1

Use of instead :

'ontouchstart' of document.documentElement

From the documentation :

You can use in to test for array presence, and of to test for JavaScript object-key presence.