Discussion on: A Clean Way to Conditionally Render Components

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Replies for: JSX will always end up with {...} somewhere. You can always use stuff like Svelte, that already includes "if" in their templating ☺️

I wanted to add the same comment about the content of the <If> being evaluated immediately
and got some quite surprising results.

See here: codesandbox.io/s/if-component-b5zxk

Anxiny • Jan 18 '22

Yes, a good example of how it works

Lou Cyx • Jan 18 '22

If you understand the underlying code for React, then this is no surprise. When you write:

import { Fragment } from "react";

const If = ({ children, condition }) =>
    condition ? <Fragment>{children}</Fragment> : undefined;

const DisplayData = ({ data }) => <Fragment>{data}</Fragment>;

const data = undefined;

export default (
    <If condition={data}>
        <DisplayData data={data} />
    </If>
);

You're actually writing this:

import { jsx } from "react/jsx-runtime";
import { Fragment } from "react";

const If = ({ children, condition }) =>
    condition ? jsx(Fragment, { children }) : undefined;

const DisplayData = ({ data }) => jsx(Fragment, { children: data });

const data = undefined;

// The important bit:
export default jsx(If, {
    condition: data,
    children: jsx(DisplayData, { data }),
});

Compared to doing it with a ternary like this:

import { Fragment } from "react";

const DisplayData = ({ data }) => <Fragment>{data}</Fragment>;

const data = undefined;

export default data ? <DisplayData data={data} /> : undefined;

That's like writing this:

import { jsx } from "react/jsx-runtime";
import { Fragment } from "react";

const DisplayData = ({ data }) => jsx(Fragment, { children: data });

const data = undefined;

// The important bit:
export default data ? jsx(DisplayData, { data }) : undefined;

With If you always call jsx with DisplayData passing data, without If you only do that call if data exists, if not you don't do anything.