Actually speaking, the question is formulated in the title of the topic?

  • id unique and class not. And an object can have several class. - gil9red

1 answer 1

  • id has a higher priority in css than class.
  • The id must be unique to the entire html document.
  • class can be combined with other classes, separated by a space, and id not.

  • id creates an object with the same name in the window space , which can be accessed via js. For example:

     <p id="some_id">Мир</p> <p id="ff-ff">Привет</p> <script> some_id.innerHTML = 'Иван'; alert(window["ff-ff"].innerHTML); </script>
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    The fourth point about the fact that an object is created is not true, check for yourself. Also according to the standard id can contain "-", which is perceived as a difference operator in js. And for good reason there is a document.getElementById() method :) - Alex
  • got it Thank you all - Muscled Boy
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    @Alex, the field with - in the title can not be accessed through a dot, otherwise it is the same field accessible through [] - Grundy
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    @Alex, added a link to a piece of the standard talking about it, if you do not believe, look there) - Duck Learns to Take Cover
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    @Alex, I also did not believe it at first, but opened the js-console and drove it in - and there is)) andreymal