第一次发现Javascript中replace() 方法如果直接用str.replace("-","!") 只会替换第一个匹配的字符.
而str.replace(/-/g,"!")则可以替换掉全部匹配的字符（g为全局标志）。
replace()
The replace() method returns the string that results when you replace text matching its first argument
(a regular expression) with the text of the second argument (a string).
If the g (global) flag is not set in the regular expression declaration, this method replaces only the first
occurrence of the pattern. For example,
var s = "Hello. Regexps are fun.";s = s.replace(/./, "!"); // replace first period with an exclamation pointalert(s);
produces the string “Hello! Regexps are fun.” Including the g flag will cause the interpreter to
perform a global replace, finding and replacing every matching substring. For example,
var s = "Hello. Regexps are fun.";s = s.replace(/./g, "!"); // replace all periods with exclamation pointsalert(s);
yields this result: “Hello! Regexps are fun!”
