How to use the ngx-custom-validators.CustomValidators.digits function in ngx-custom-validators

},
    base64: {
      func: CustomValidators.base64,
      params: ["min"]
    },
    creditCard: {
      func: CustomValidators.creditCard
    },
    date: {
      func: CustomValidators.date
    },
    dateISO: {
      func: CustomValidators.dateISO
    },
    digits: {
      func: CustomValidators.digits
    },
    equal: {
      func: CustomValidators.equal,
      params: ["equal"]
    },
    equalTo: {
      func: CustomValidators.equalTo,
      params: ["equalTo"]
    },
    gt: {
      func: CustomValidators.gt,
      params: ["gt"]
    },
    gte: {
      func: CustomValidators.gte,
      params: ["gte"]