React.js：在页面上插入新表单字段时如何防止浪费渲染

Question

I have a form with a couple of conditionally rendered fields. The form is made up of MUI components, react-hook-form and yup for its validation.

Additionally, I have added a console.log() within the AutocompleteCoffee , RadioBtnGroup , TxtField components that will execute every time the components are rendered.

Scenario

When the page loads you can see a log from each component. Nothing new here.

When you select "Yes" from, Do you like coffee? a new field will be rendered. This action triggers a rerender of all the components on the page.

I am using the watch method from react-hook-form to keep track of the question mentioned above.

const coffee = watch("coffee", "No");
...
{coffee === "Yes" ? (
          <AutocompleteCoffee
            required
            fullWidth
            name="coffeType"
            label="Which coffee type"
            control={control}
            options={coffeList}
            error={!!errors.coffeType}
            helperText={errors?.coffeType?.message}
          />
        ) : null}
...

You can see the working CodeSandbox here .

Question

I was wondering how to prevent all the wasted renders. Any ideas?

Thank you in advance!

Answer 1

I've got this performance issue once. As per docs , you should switch to callback way of calling watch or to useWatch

This API will trigger re-render at the root of your app or form, 
consider using a callback or the useWatch API
if you are experiencing performance issues.

code would look like:

instead of your coffee check, do <MaybeCoffee control={control} errors={errors} /> and remove watch("coffee", "No") as well.

Then add a component MaybeCoffee:

const MaybeCoffee = ({ control, errors }) => {
  const coffee = useWatch({ control, name: "coffee" }) || "No";
  return coffee === "Yes" ? (
    <AutocompleteCoffee
      required
      fullWidth
      name="coffeType"
      label="Which coffes type"
      control={control}
      options={coffeList}
      error={!!errors.coffeType}
      helperText={errors?.coffeType?.message}
    />
  ) : null;
}

an example https://codesandbox.io/s/testing-rerenders-forked-19invg?file=/src/components/MainForm.js