Why don't browsers throw an error when any other word is used in place of 'javascript' in the value of onclick?
Solution 1:
The string value of an "onclick" attribute is taken to be simple JavaScript code. JavaScript includes provisions for labeled statements, so that code is a return statement with the label "jamoscript". In other words, this:
jamoscript: return confirm("Do you really want to hurt me?");
is perfectly legal JavaScript. Labels aren't used much, so they're unfamiliar.
The only context in which the "javascript:" prefix matters is when a URL is expected, as is the case with the "href" attribute of <a> tags.