==============================[br]eval 函数[br]功能：先解释javascript代码，然后在执行它[br]用法：eval(codestring)[br]codestring是包含有javascript语句的字符串，在eval之后使用javascript引擎编译。[br][br]注释：[br][br]例子：eval(id + "_icon.src="/imgs/collapse_up.gif'");[br]id是之前设定的参数，而在双引号中的字符串则是需要编译的[br][br]引用:[br]--------------------------------------------------------------------------------[br]function tophide(id) //id indicates menu[br]{[br] if (top.topframeset.rows == "31,*")[br] {[br] top.topframeset.rows = "86,*";[br] eval(id + "_icon.src="/imgs/collapse_up.gif'");[br] eval(id + "_icon.alt='collapse the head'");[br] head.style.display = "block"[br] }[br] else[br] {[br] top.topframeset.rows = "31,*";[br] eval(id + "_icon.src="/imgs/collapse_down.gif'");[br] eval(id + "_icon.alt='expand the head'");[br] head.style.display = "none"[br] }[br]}