// NOTE: only escapes a " if it's not already escaped
function escapeDoubleQuotes(str) {
	return str.replace(/\\([\s\S])|(")/g,"\\$1$2"); // thanks @slevithan!
}

escapeDoubleQuotes("ab");   // ab  =>  ab
escapeDoubleQuotes("a\"b");   // a"b  =>  a\"b
escapeDoubleQuotes("a\\\"b");   // a\"b  =>  a\"b
escapeDoubleQuotes("a\\\\\"b");   // a\\"b  =>  a\\\"b
escapeDoubleQuotes("a\\\\\\\"b");   // a\\\"b  =>  a\\\"b

escapeDoubleQuotes("a\"b\"c");   // a"b"c  =>  a\"b\"c
escapeDoubleQuotes("a\"\"b");   // a""b  =>  a\"\"b
escapeDoubleQuotes("\"\"");   // ""  =>  \"\"

// don't unnecessarily escape:
escapeDoubleQuotes(escapeDoubleQuotes(escapeDoubleQuotes("a\"b"))); // a"b  =>  a\"b