JavaScript

  JavaScript - Fundamental 3 ways to use JavaScript Embedded in html (inline) - not recommend < body >   < a href = "javascript:alert('hello')" > click </ a > </ body > Internal < body >   < script >   alert ( "hello" ) </ script >   </ body >   External < body >   < script scr = "js/hello.js" ></ script > </ body > alert ( "Hi there!" ) JavaScript syntax // print console . log () //dialog alert（ "hello" ） // write content to html page document . write ( "hello" ) // get data type - typeof var num   = 'xx' console . log ( typeof num ) //out: string JavaScropt data types number var num = 10; string var sex = 'male' ; var sex = "female" ; boolean var flag1 = true ; var flag2 = false ; undefined and null (2 special types in Js) object - complex type（a collection of various values） Narrow object va...