recma-mdx-escape-missing-components

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This package is a unified (recma) plugin which allows you to escape MDX components that are either missing or not provided in an MDX document.

unified is a project that transforms content with abstract syntax trees (ASTs) using the new parser micromark. recma adds support for producing a javascript code by transforming esast which stands for Ecma Script Abstract Syntax Tree (AST) that is used in production of compiled source for the MDX.

When should I use this?

This plugin is useful for escaping MDX components that are missing or not explicitly provided in your MDX document.

You won’t encounter errors for missing or undefined MDX components because recma-mdx-escape-missing-components assigns a default value of () => null for them.

Installation

This package is suitable for ESM only. In Node.js (version 18+), install with npm:

npm install recma-mdx-escape-missing-components

or

yarn add recma-mdx-escape-missing-components

Usage

Say we have the following file, example.mdx, which consists some mdx components.

# Hi

<Component1 />

<Component2 />

And our module, example.js, looks as follows:

import { read } from "to-vfile";
import { compile } from "@mdx-js/mdx";
import recmaMdxEscapeMissingComponents from "recma-mdx-escape-missing-components";

main();

async function main() {
  const source = await read("example.mdx");

  const compiledSource = await compile(source, {
    recmaPlugins: [recmaMdxEscapeMissingComponents],
  });

  return String(compiledSource);
}

Now, running node example.js produces the compiled source which contains the statement below:

// ...
const _EmptyComponent = () => null;
function _createMdxContent(props) {
  // ...
  const {Component1 = _EmptyComponent, Component2 = _EmptyComponent} = _components;
  // ...
}

Without the recma-mdx-escape-missing-components, you’d not get any Empty Component definition and default value for the components:

// ...
function _createMdxContent(props) {
  // ...
  const {Component1, Component2} = _components;
  // ...
}

Basically, the recma-mdx-escape-missing-components;

🟩 inserts an Empty Component definition into the code above the function _createMdxContent(props){}

const _EmptyComponent = () => null;

🟩 looks for a declaration statement in an object pattern initiated by the _components

const {Component1, Component2} = _components;

🟩 converts it as the destructed components have a default value _EmptyComponent

const {Component1 = _EmptyComponent, Component2 = _EmptyComponent} = _components;

Options

type TestFunction = (componentName: string) => boolean | undefined | null;

function recmaMdxEscapeMissingComponents(test?: string | string[] | TestFunction)

test

• if "undefined", all components pass the check.
• if "string", check the component name matches with the string.
• if "string[]", check the component name is included in the string array.
• if "TestFunction", check the test function returns true.
• if check is true/pass, set the default value () => null for that component.

Examples:

# Hi

<Component1 />

Wellcome

<Component2 />

Without the test option

use(recmaMdxEscapeMissingComponents);

is going to produce the compiled source has the statement for all components have the default value:

const {Component1 = _EmptyComponent, Component2 = _EmptyComponent} = _components;

With the test option (string)

use(recmaMdxEscapeMissingComponents, "Component1");

is going to produce the compiled source has the statement for only the Component1 has the default value:

const {Component1 = _EmptyComponent, Component2} = _components;

With the test option (string array)

use(recmaMdxEscapeMissingComponents, ["Component1"]);

is going to produce the compiled source has the statement for only the Component1 has the default value:

const {Component1 = _EmptyComponent, Component2} = _components;

With the test option (function)

use(recmaMdxEscapeMissingComponents, ((name) => name.endsWith("2")) as TestFunction);

is going to produce the compiled source has the statement for only the Component2 has the default value:

const {Component1, Component2 = _EmptyComponent} = _components;

Syntax tree

This plugin only modifies the ESAST (Ecma Script Abstract Syntax Tree) as explained.

Types

This package is fully typed with TypeScript. Test function in the option is exported as type TestFunction.

Compatibility

This plugin works with unified version 6+. It is compatible with mdx version 3+.

Security

Use of recma-mdx-escape-missing-components doesn't involve user content so there are no openings for cross-site scripting (XSS) attacks.

My Plugins

I like to contribute the Unified / Remark / MDX ecosystem, so I recommend you to have a look my plugins.

My Remark Plugins

• remark-flexible-code-titles – Remark plugin to add titles or/and containers for the code blocks with customizable properties
• remark-flexible-containers – Remark plugin to add custom containers with customizable properties in markdown
• remark-ins – Remark plugin to add ins element in markdown
• remark-flexible-paragraphs – Remark plugin to add custom paragraphs with customizable properties in markdown
• remark-flexible-markers – Remark plugin to add custom mark element with customizable properties in markdown
• remark-flexible-toc – Remark plugin to expose the table of contents via vfile.data or via an option reference
• remark-mdx-remove-esm – Remark plugin to remove import and/or export statements (mdxjsEsm)

My Rehype Plugins

• rehype-pre-language – Rehype plugin to add language information as a property to pre element
• rehype-highlight-code-lines – Rehype plugin to add line numbers to code blocks and allow highlighting of desired code lines

My Recma Plugins

• recma-mdx-escape-missing-components – Recma plugin to set the default value () => null for the Components in MDX in case of missing or not provided so as not to throw an error
• recma-mdx-change-props – Recma plugin to change the props parameter into the _props in the function _createMdxContent(props) {/* */} in the compiled source in order to be able to use {props.foo} like expressions. It is useful for the next-mdx-remote or next-mdx-remote-client users in nextjs applications.

License

MIT License © ipikuka