JavaScript Advanced Programming 01-Basic concepts

One, JavaScript composition

1. A finished javascript is composed of three parts: ECMAScript, DOM, and BOM.

ECMAScript: Provides core language functions-grammar, type, statement, keyword, reserved word, operator, object;

DOM: Document Object Model-provides methods and interfaces for accessing and manipulating Web page content;

BOM: Browser Object Model--provides methods and interfaces for interacting with the browser

Second, reference JS in the page

1. There are two ways to refer to JS in a Web page--Embedding and external

<! DOCTYPE html>function  helloWorld () {        alert (' I am rookie ~ ~ ')    }    HelloWorld (); </script>
2.<noscript> elements
As the name implies, no script means! When did it happen? The browser does not support scripts or browser support scripts, but the script is disabled!
<! DOCTYPE html>
JavaScript Advanced Programming 01-Basic concepts