限制输入负数及超过两位小数。

oninput="this.value=this.value.replace(/[^\d.]/g,'').replace(/^\./g,'').replace(/\.{2,}/g,'.')
.replace('.','$#$').replace(/\./g,'').replace('$#$','.').replace(/^(\-)*(\d+)\.(\d\d).*$/,'$1$2.$3')"