验证是否为数字

function verifyNumber(value) {
  let reg = /^[+]{0,1}(d+)$|^[+]{0,1}(d+.d+)$/;
  let lastChar = value.substr(value.length - 1);
  return reg.test(lastChar) || value === "";
}


 verifyNumber("-1")  //true
 verifyNumber("+1")  //true
 verifyNumber("1")   //true
 verifyNumber("1a")  //false