如何使用 JavaScript 方法 hasFocus() 不是在整个文档上而是在文档内的元素上？

Question

The definition on w3schools says that it can be done, but nowhere it's shown how. Snippet:

if (document.getElementById(atr).hasFocus())
{
  console.log("focused");
}
else
{
  console.log("not focused");
}

Answer 1

I feel this is down to a misreading of the document. The doc says:

The hasFocus() method returns a Boolean value indicating whether the document (or any element inside the document) has focus.

It is not saying that you can check either the document, or any element you want, instead it is saying it will check if the document or any element inside the document has focus

---

To propose a method with similiar functionality you can simply compare document.activeElement with your chosen element

// Get Element
let testElement = document.getElementById('container');

// Check against .activeElement
let isFocused = (document.activeElement === dummyEl);

Answer 2

document.activeElement是焦点元素，您可以通过===来检查活动元素，例如document.activeElement === document.getElementById('idOfYourHtmlElement')默认情况下，活动元素为body

Answer 3

To do the hasFocus method on an element, you first need to select it like so document.getElementById(elementId) and then put that in a variable to make it easier such as let testElement = document.getElementById(elementId) and then test this element with the hasFocus method as seen below

 if(document.activeElement == testElement){ //DO something... }