Regular expression substitution string [javascript]__ regular expression

Requirements: "Ice \ Rain three Liu De \\\" Hua-----\\12 rain 3\\\\\\\\\\222222 "" \ "replaced by a | | and is only to replace \, can not replace more than two characters, for example, should only replace the ice rain between the middle of \ and--12 \.

Regular expression is my old friend, like it is about 07 time processing a publishing system tag read items, a long time useless, a little rusty. Encountered the problem of string processing, my first thought must be regular expression, eclipse also standing a regular plug-in, simple thinking after the:

Move directly to JavaScript and find that JavaScript does not support the writing of (? <!), that is, "reverse negation", which can only be done in other ways, and has:

	function Change (newstr) {
		//var reg =/(? <!\\) \\\\ (?! \)/g;
		var reg =/[^\\] (\\{2}) (?! \)/g;
		var str_before = ' ice \ Rain three Liu De \\\ ' hua-----\\12 rain 3\\\\\\\\\\222222 ';
		var str_before = ' Ice \\\\ rain three Liu De \\\\\\ ' hua-----\\\\12 rain 3\\\\\\\\\\\\\\\\\\\\222222 ';
		var str_after = Str_before.replace (REG,NEWSTR);
		alert (str_after);
	}

Write like this, not only will meet the conditions of the capture, will also be the front of a character capture to the brain a bit not bright, think for a long time, did not come up with a good method, and finally reverse thinking a bit, the character extracted and to replace the word is not a match. So there was:

	function Change (newstr) {
		//var reg =/(? <!\\) \\\\ (?! \)/g;
		var reg =/[^\\] (\\{2}) (?! \)/g;
		var str_before = ' ice \ Rain three Liu De \\\ ' hua-----\\12 rain 3\\\\\\\\\\222222 ';
		var str_before = ' Ice \\\\ rain three Liu De \\\\\\ ' hua-----\\\\12 rain 3\\\\\\\\\\\\\\\\\\\\222222 ';
		var str_after = str_before.replace (Reg, function (m) {
			m = m.substring (0, 1);
			return m + newstr;
		});
		alert (str_after);
	}

Basically meet the demand.