Javascript efficiently identifies the browser type and version

<SCRIPT type = "text/JavaScript">
VaR sys = {};
VaR UA = navigator. useragent. tolowercase ();
VaR S;
(S = UA. Match (/MSIE ([\ D.] + )/))? SYS. Ie = s [1]:
(S = UA. Match (/Firefox \/([\ D.] + )/))? SYS. Firefox = s [1]:
(S = UA. Match (/chrome \/([\ D.] + )/))? SYS. Chrome = s [1]:
(S = UA. Match (/opera. ([\ D.] + )/))? SYS. Opera = s [1]:
(S = UA. Match (/version \/([\ D.] +). * Safari /))? SYS. Safari = s [1]: 0;

// Perform the following tests:
If (SYS. ie) document. Write ('ie: '+ SYS. ie );
If (SYS. Firefox) document. Write ('Firefox: '+ SYS. Firefox );
If (SYS. Chrome) document. Write ('chrome: '+ SYS. Chrome );
If (SYS. Opera) document. Write ('Opera: '+ SYS. Opera );
If (SYS. Safari) document. Write ('safari: '+ SYS. Safari );
</SCRIPT>

In this example, "...?" is used. ...:... "To streamline the code. The judgment condition is a value assignment statement that completes Regular Expression matching and result copying, and directly serves as a condition judgment. The subsequent version information only needs to be extracted from the previous matching results, which is a very efficient code.

The above code is pre-developed to build a front-end framework and tested on five browsers. In the future, to judge a browser, you only need to use if (sys. IE) or if (sys. to determine the browser version, you only need to use if (sys. ie = '8. 0 ') or if (sys. firefox = '3. 0.

Then change the browser to preview the effect.