1, <scrpit> </ script> tags was introduced in the HTML tags js code for, have the following characteristics: async (characteristic value indicates whether the immediately download the resource is introduced external files, and can not affect the page other operations is an asynchronous operation will be performed before the load event), charset (code indicating the character set), defer (such as page represents all structures appear after re-execute the file js code), type (equivalent substitute language), src (introduction file the address of)
2, the introduction js files in two ways, one is introduced at the beginning of the file (now generally placed behind the <body> element), this time for the essential characteristics of the src and if re-write the code in the script tags will be ignored internal a html page when embedding, it is necessary at this time type characteristics, introduction file, the execution code sequence, and will interrupt page processing, recommended introducing js file
3, the document has promiscuous mode and standard mode, the default document is promiscuous mode
4, <noscript> </ noscript> will not support the browser or disable js js script shows