How to validate using yup to check string min length, max length and allow empty-CodePudding

firstName: yup
    .string()
    .test(
        'len',
        'can be empty or with string at least 2 characters and not more than 10',
        (val) => val != undefined && (val.length == 0 || (val.length >= 2 && val.length <= 10) )
    )

in this case length min 2 and max 10 works, but when is empty is marked with error i tried with val.length == 0

CodePudding user response：

fixed by separate undefined check

  firstName: yup
            .string()
            .test(
                'len',
                'can be empty or with string at least 2 characters and not more than 10',
                (val) => {
                    if (val == undefined) {
                        return true;
                    }
                    return  ((val.length == 0 || (val.length >= 2 && val.length <= 10)))
                }
            ),

CodePudding user response：

Hello you can do it like this

const yup = require("yup");
const firstName = "";

const schema = yup
  .string()
  .test(
    "len",
    "can be empty or with string at least 2 characters and not more than 10",
    (val) => {
      if (val === undefined) {
        return true;
      }
      return val.length === 0 || (val.length >= 2 && val.length <= 10);
    }
  );

schema
  .validate(firstName)
  .then((response) => console.log(response))
  .catch((err) => console.log(err));