datocms-contentful-to-structured-text

This package contains utilities to convert Contentful Rich Text to a DatoCMS Structured Text dast (DatoCMS Abstract Syntax Tree) document.

Please refer to the dast format docs to learn more about the syntax tree format and the available nodes.

Usage

The main utility in this package is richTextToStructuredText which takes a Rich Text JSON and transforms it into a valid dast document.

richTextToStructuredText returns a Promise that resolves with a Structured Text document.

import { richTextToStructuredText } from 'datocms-contentful-to-structured-text';

const richText = {
  nodeType: 'document',
  data: {},
  content: [
    {
      nodeType: 'heading-1',
      content: [
        {
          nodeType: 'text',
          value: 'Lorem ipsum dolor sit amet',
          marks: [],
          data: {},
        },
      ],
      data: {},
    },
};

richTextToStructuredText(richText).then((structuredText) => {
  console.log(structuredText);
});

Validate dast documents

dast is a strict format for DatoCMS' Structured Text fields and follows a different pattern from Contentful Rich Text structure.

The datocms-structured-text-utils package provides a validate utility to validate a Structured Text content to make sure that it is compatible with DatoCMS' Structured Text field.

import { validate } from 'datocms-structured-text-utils';

// ...

richTextToStructuredText(richText).then((structuredText) => {
  const { valid, message } = validate(structuredText);

  if (!valid) {
    throw new Error(message);
  }
});

We recommend to validate every dast to avoid errors later when creating records.

Advanced Usage

Options

All the *ToStructuredText utils accept an optional options object as second argument:

type Options = Partial<{
  // Override existing Contentful node handlers or add new ones.
  handlers: Record<string, CreateNodeFunction>,
  // Array of allowed Block nodes.
  allowedBlocks: Array<
    BlockquoteType | CodeType | HeadingType | LinkType | ListType,
  >,
  // Array of allowed marks.
  allowedMarks: Mark[],
}>;

Transforming Nodes

The utils in this library traverse a Contentful Rich Text tree and transform supported nodes to dast nodes. The transformation is done by working on a Contentful Rich Text node with a handler (async) function.

Handlers are associated to Contentful Rich Text nodes by nodeType and look as follow:

import { visitChildren } from 'datocms-contentful-to-structured-text';

// Handler for the paragraph node type.
async function p(createDastNode, contentfulNode, context) {
  return createDastNode('paragraph', {
    children: await visitChildren(createDastNode, contentfulNode, context),
  });
}

Handlers can return either a promise that resolves to a dast node, an array of dast Nodes, or undefined to skip the current node.

To ensure that a valid dast is generated, the default handlers also check that the current contentfulNode is a valid dast node for its parent and, if not, they ignore the current node and continue visiting its children.

Information about the parent dast node name is available in context.parentNodeType.

Please take a look at the default handlers implementation for examples.

The default handlers are available on context.defaultHandlers.

Context

Every handler receives a context object containing the following information:

export interface Context {
  // The current parent `dast` node type.
  parentNodeType: NodeType;
  // The parent `Contentful Rich Text` node.
  parentNode: ContentfulNode;
  // A reference to the current handlers - merged default + user handlers.
  handlers: Record<string, Handler<unknown>>;
  // A reference to the default handlers record (map).
  defaultHandlers: Record<string, Handler<unknown>>;
  // Marks for span nodes.
  marks?: Mark[];
  // Array of allowed Block types.
  allowedBlocks: Array<
    BlockquoteType | CodeType | HeadingType | LinkType | ListType,
  >;
  // Array of allowed marks.
  allowedMarks: Mark[];
}

Custom Handlers

It is possible to register custom handlers and override the default behaviour via options, using the makeHandler function.

For example, to create a custom handler for the Contentful text element, specify a guard clause to specify the correct type

  import { makeHandler } from 'datocms-contentful-to-structured-text';

  const customTextHandler = makeHandler(
    (node): node is Text => n.nodeType === "text",
    async (node) => {
      // This custom handler will generate two spans for every text node, instead of one.
      return [
        { type: 'span', value: node.value },
        { type: 'span', value: node.value },
      ];
    }),

  richTextToStructuredText(richText, {
    handlers: [
      customTextHandler,
    ],
  }).then((structuredText) => {
    console.log(structuredText);
  });

import { paragraphHandler } from './customHandlers';

richTextToStructuredText(richText, {
  handlers: {
    paragraph: paragraphHandler,
  },
}).then((structuredText) => {
  console.log(structuredText);
});

It is highly encouraged to validate the dast when using custom handlers because handlers are responsible for dictating valid parent-children relationships and therefore generating a tree that is compliant with DatoCMS Structured Text.

Preprocessing Rich Text

Because of the strictness of the dast spec, it is possible that some elements might be lost during transformation.

To improve the final result, you might want to modify the Rich Text tree before it is transformed to dast.

Examples

In dast, images can only be presented as Block nodes, but blocks are not allowed inside of ListItem nodes (unordered-list/ordered-list). In this example we will split the original unordered-list in one list, the lifted up image block and another list.

import { liftAssets } from 'datocms-contentful-to-structured-text';

const richTextWithAssets = {
  nodeType: 'document',
  data: {},
  content: [
    {
      nodeType: 'unordered-list',
      content: [
        {
          nodeType: 'list-item',
          content: [
            {
              nodeType: 'paragraph',
              content: [
                {
                  nodeType: 'text',
                  value: 'text',
                  marks: [],
                  data: {},
                },
              ],
              data: {},
            },
            {
              content: [],
              data: {
                target: {
                  sys: {
                    id: 'zzz',
                    linkType: 'Asset',
                    type: 'Link',
                  },
                },
              },
              nodeType: 'embedded-asset-block',
            },
            {
              nodeType: 'paragraph',
              content: [
                {
                  nodeType: 'text',
                  value: 'text',
                  marks: [],
                  data: {},
                },
              ],
              data: {},
            },
          ],
          data: {},
        },
      ],
      data: {},
    },
  ],
};

liftAssets(richTextWithAssets);

const handlers = {
  'embedded-asset-block': async (createNode, node, context) => {
    const item = '123';
    return createNode('block', {
      item,
    });
  },
};

const dast = await richTextToStructuredText(richTextWithAssets, { handlers });

The liftAssets function transforms the richText tree and moves the embedded-asset-block to root,splitting the list in two parts.

function liftAssets(richText) {
  const visit = (node, cb, index = 0, parents = []) => {
    if (node.content && node.content.length > 0) {
      node.content.forEach((child, index) => {
        visit(child, cb, index, [...parents, node]);
      });
    }

    cb(node, index, parents);
  };

  const liftedImages = new WeakSet();

  visit(richText, (node, index, parents) => {
    if (
      !node ||
      node.nodeType !== 'embedded-asset-block' ||
      liftedImages.has(node) ||
      parents.length === 1 // is a top level asset
    ) {
      return;
    }

    const imgParent = parents[parents.length - 1];

    imgParent.content.splice(index, 1);

    let i = parents.length;
    let splitChildrenIndex = index;
    const contentAfterSplitPoint = [];

    while (--i > 0) {
      const parent = parents[i];
      const parentsParent = parents[i - 1];

      contentAfterSplitPoint = parent.content.splice(splitChildrenIndex);

      splitChildrenIndex = parentsParent.content.indexOf(parent);

      let nodeInserted = false;

      if (i === 1) {
        splitChildrenIndex += 1;
        parentsParent.content.splice(splitChildrenIndex, 0, node);
        liftedImages.add(node);

        nodeInserted = true;
      }

      splitChildrenIndex += 1;

      if (contentAfterSplitPoint.length > 0) {
        parentsParent.content.splice(splitChildrenIndex, 0, {
          ...parent,
          content: contentAfterSplitPoint,
        });
      }
      // Remove the parent if empty
      if (parent.content.length === 0) {
        splitChildrenIndex -= 1;
        parentsParent.content.splice(
          nodeInserted ? splitChildrenIndex - 1 : splitChildrenIndex,
          1,
        );
      }
    }
  });
}

License

MIT