正则匹配输入小数点后两位，

var a = document.getElementsByTagName('input')
function dianwo(e) {
var value = a[0].value
value = value.replace(/[^\d.]/g, '').replace(/.{2,}/g, '.').replace('.', '$#$').replace(/./g, '').replace('$#$', '.').replace(/^(-)(\d+).(\d\d).$/, '$1$2.$3').replace(/^./g, '')
console.log(value)
// console.log(value)
}