What is BOM?

BOM is another object model after learning the DOM document object model--------- browser object model, which provides a series of objects that interact with the browser window independently of content, and each object There are many methods and properties, the core object and the top-level object are window 

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Let's review the difference between DOM and BOM:

DOM：

• Document Object Model
• The top-level object is document
• The main learning content is to operate page elements
• The standard is the W3C standard specification

BOM：

• Browser Object Model
• The top-level object is window
• The main learning is the interaction of the browser window
• BOM is set by browser manufacturers in their respective browsers, and the compatibility is very poor

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We need to understand clearly: BOM is bigger than DOM, DOM is contained in BOM

The window object is the top-level object of the browser. It is not only an interface for JS to access the browser , but also a global object . Variables and functions defined in the global scope will become a method of it: but when calling, we usually To save window, just console.log(a) directly. For example, I am from Henan. When I tell others about my province, I don’t need to say that I am from Henan, China.

 <script>
      var a=100;
      console.log(window.a);
    </script>