Monday, 12 November 2018

Formik

Formik is a brilliant React form builder.  It is simple and intuitive.  It includes validation using a third party - I'm using yup below.

Basic Formik

This example below shows the basics of using Formik.  The internal properties and functions of formik take care of all the plumbing.  All you need to do is wire the onChange and onBlur functions to the individual 

<div>
  <Formik
    initialValues={{
      title: '',
      firstName: '',
      surname: ''
    }}
    validationSchema={Yup.object().shape({
      title: Yup.string()
        .trim()
        .required('Please enter a title')
        .max(5, 'Too many characters (Maximum 5 allowed)'),
      firstName: Yup.string()
        .trim()
        .required('Please enter a firstName')
        .max(100, 'Too many characters (Maximum 100 allowed)'),
      surname: Yup.string()
        .trim()
        .required('Please enter a surname')
        .max(100, 'Too many characters (Maximum 100 allowed)'),
      
    })}
    onSubmit={values => alert(values)}
  >
    {formikProps => {
      const {
        values,
        touched,
        errors,
        isSubmitting,
        handleChange,
        handleBlur,
        handleSubmit,
        setFieldValue,
        setFieldTouched
      } = formikProps
      return (
        <form>
          <div>
            <label htmlFor="title">
              <span className="mandatory">Title</span>
              <input
                id="title"
                type="text"
                value={values.title}
                onChange={handleChange}
                onBlur={handleBlur}
                className={`${errors.title && touched.title ? error : ''}`}
              />      
              {errors.title && touched.title && <div>{errors.title}</div>}
            </label>
          </div>

          <div>
            <label htmlFor="firstName">
              <span className="mandatory">First Name</span>
              <input
                id="firstName"
                type="text"
                value={values.firstName}
                onChange={handleChange}
                onBlur={handleBlur}
                className={`${errors.firstName && touched.firstName ? error : ''}`}
              />      
              {errors.firstName && touched.firstName && <div>{errors.firstName}</div>}
            </label>
          </div>

          <div>
            <label htmlFor="surname">
              <span className="mandatory">Surname</span>
              <input
                id="surname"
                type="text"
                value={values.surname}
                onChange={handleChange}
                onBlur={handleBlur}
                className={`${errors.surname && touched.surname ? error : ''}`}
              />      
              {errors.surname && touched.surname && <div>{errors.surname}</div>}
            </label>
          </div>
        </form>
      )
    }}
  </Formik>
</div>


Validate on Edit

By default Formik will validate once the first blur has occurred and then everytime on change.  This gives the user the chance to get the content right first without being bothered by error messages.  However, should you want to validate all changes from the off you can change your inputs to include an onInput function,


            <label htmlFor="surname">

              <span className="mandatory">Surname</span>
              <input
                id="surname"
                type="text"
                value={values.surname}

                onInput={() => setFieldTouched('surname', true)} // Validate as the user types
                onChange={handleChange}
                onBlur={handleBlur}
                className={`${errors.surname && touched.surname ? error : ''}`}
              />      
              {errors.surname && touched.surname && <div>{errors.surname}</div>}
            </label>


Validate Function

Validation doesn't have to be done by a schema.  This is quite limiting as it doesn't allow dynamic messages to be generated.  You can still use a schema as this is really easy syntax but just recreate it each time.  If you use the validate function the Formik 'values' object is passed to it.  This can be used to generate a schema with the current values and adjust the error messages accordingly.  In the example below the validate function calls for a validationSchema.  The schema uses the values and the ` string template indicator to create dynamic error messaages.

getValidateSchema = values => 
  Yup.object().shape({
    title: Yup.string()
      .trim()
      .required('Please enter a title')
      .max(5, `Too many characters (${values.title.length} entered, Maximum 5 allowed)`),
    firstName: Yup.string()
      .trim()
      .required('Please enter a firstName')
      .max(100, `Too many characters (${values.firstName.length} entered, Maximum 100 allowed)`),
    surname: Yup.string()
      .trim()
      .required('Please enter a surname')
      .max(100, `Too many characters (${values.surname.length} entered, Maximum 100 allowed)`),
  })

validate = values => {
  try {
    validateYupSchema(values, this.getValidateSchema(values), true, {})
    return {}
  } catch (error) {
    return yupToFormErrors(error)
  }
}

render = () => 
  <div>
    <Formik
      initialValues={{
        title: '',
        firstName: '',
        surname: ''
      }}
      validate={values => this.validate(values)}
      onSubmit={values => alert(values)}
    >
      {formikProps => {
        const {
          values,
          touched,
          errors,
          isSubmitting,
          handleChange,
          handleBlur,
          handleSubmit,
          setFieldValue,
          setFieldTouched
        } = formikProps
        return (
          <form>
            <div>
              <label htmlFor="title">
                <span className="mandatory">Title</span>
                <input
                  id="title"
                  type="text"
                  value={values.title}
                  onInput={() => setFieldTouched('title', true)}
                  onChange={handleChange}
                  onBlur={handleBlur}
                  className={`${errors.title && touched.title ? error : ''}`}
                />      
                {errors.title && touched.title && <div>{errors.title}</div>}
              </label>
            </div>

            <div>
              <label htmlFor="firstName">
                <span className="mandatory">First Name</span>
                <input
                  id="firstName"
                  type="text"
                  value={values.firstName}
                  onInput={() => setFieldTouched('firstName', true)}
                  onChange={handleChange}
                  onBlur={handleBlur}
                  className={`${errors.firstName && touched.firstName ? error : ''}`}
                />      
                {errors.firstName && touched.firstName && <div>{errors.firstName}</div>}
              </label>
            </div>

            <div>
              <label htmlFor="surname">
                <span className="mandatory">Surname</span>
                <input
                  id="surname"
                  type="text"
                  value={values.surname}
                  onInput={() => setFieldTouched('surname', true)}
                  onChange={handleChange}
                  onBlur={handleBlur}
                  className={`${errors.surname && touched.surname ? error : ''}`}
                />      
                {errors.surname && touched.surname && <div>{errors.surname}</div>}
              </label>
            </div>
          </form>
        )
      }}
    </Formik>
  </div>

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