const digitsRE = /(\d{3})(?=\d)/g

export function currency (value, currency, decimals) {

  value = parseFloat(value)

  if (!isFinite(value) || (!value && value !== 0)) return ''

  currency = currency != null ? currency : '$'

  decimals = decimals != null ? decimals : 2

  var stringified = Math.abs(value).toFixed(decimals)

  var _int = decimals

    ? stringified.slice(0, -1 - decimals)

    : stringified

  var i = _int.length % 3

  var head = i > 0

    ? (_int.slice(0, i) + (_int.length > 3 ? ',' : ''))

    : ''

  var _float = decimals

    ? stringified.slice(-1 - decimals)

    : ''

  var sign = value < 0 ? '-' : ''

  return sign + currency + head +

    _int.slice(i).replace(digitsRE, '$1,') +

    _float

}

import {currency} from './../util/currency'

  filters:{

      currency:currency

    },

  <div class="item-total">

                Item total: <span class="total-price">{{totalPrice|currency('$')}}</span>

              </div>

import  {currency} from './util/currency'

Vue.filter("currency",currency);

<div class="cart-tab-4">

         <div class="item-price-total">{{(item.productNum*item.salePrice)|currency('$')}}</div>

 </div>