问题
Below is some sample code.
<body>
<div id="wrapper" class="access">
<form id="test">
<input id="password"></input>
<input type="submit"></input>
</form>
</div>
<script>
console.log(password);
alert(wrapper.className);
</script>
</body>
The console log returns the DOM element with id password. The alert is "alert".
It works in normal code as well, e.g. var x = wrapper.className;
Surely this is not right? What is the point of document.getElementById, $('#password') or goog.dom.getElement if it just works like this? Are these functions just for legacy now?
It works in Firefox, Chrome and Safari, incidentally.
回答1:
This answer should give you a lot to go on:
https://stackoverflow.com/a/6381766/944006
You shouldn't use these variables, and you DEFINITELY don't want to depend on them working correctly across browsers.
回答2:
Backwards compatibility is the reason IDs are mapped to properties of the window.
It's also a major reason to avoid global variables - in fact some browsers will outright break if you try to use a global variable that's the same name as an element's ID.
来源：https://stackoverflow.com/questions/23121526/javascript-access-dom-elements-without-getelementbyid