两位小数，纯数字

*纯数字

onkeyup="this.value=this.value.replace(/\D/g,'')"

*长度

onkeyup="this.value.length == 11"

*两位小数

onkeyup="this.value=this.value.replace(/^(\-)*(\d+)\.(\d\d).*$/,'$1$2.$3','')"