javascript: is the default action when triggered, execute JavaScript code, and execute javascript :; represent nothing, nothing happens when you click on this.
<a href="www.baidu.com"> </a> this refers to a label, then click the jump to Baidu Home
<a href="javascript:;"> </a> click is not going to jump, generally used for the development of the page has not been completed.
href = "javascript :;" is to remove the default behavior of a tag with href = "javascript: void (0)" is the same, void of JavaScript is an operator, void (0) is to do nothing means
Briefly, "javascript:" is another method js code page nested.
By nesting js code label with the same.
<a href = "javascript:alert(22);"> point I </a>
If you do not enter JS content
<a href = "javascript:;"> </a> point I
said nothing execution