React Substitute

Highly configurable placeholder substitution for React: replace {placeholders} in a string using values from a context object or render the result as React nodes (with component placeholders like <0>...</0>).

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Features

• Replace {placeholders} using a context object (supports nested objects via dot-path keys)
• Optional transform() hook for custom replacement logic
• Supports modifiers and a single item-level context inside placeholders
• Can return either a string or React nodes
• Customizable placeholder separators and RegExp pattern

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Install

npm i @vojtechportes/react-substitute
# or
yarn add @vojtechportes/react-substitute

Node: >= 10

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Quick start (string output)

import { reactSubstitute } from '@vojtechportes/react-substitute';

const text = 'Hello {user.name}! You have {count} messages.';

const out = reactSubstitute(text, {
  context: {
    user: { name: 'John' },
    count: 3,
  },
});

console.log(out);
// "Hello John! You have 3 messages."

Nested objects are flattened internally, so {user.name} works out of the box.

Unmatched placeholders are replaced with an empty string by default.

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Placeholder syntax

Default format:

• {key}
• {key|modifier1|modifier2:context}

Defaults: - modifierSeparator: | - contextSeparator: : - pattern: /\{([^{}]+)\}/g

Modifiers

Everything after | is collected into modifiers: string[] and passed to transform().

Item-level context

Only one context segment is supported (after :). If more are present, only the first is used.

contextType options:

• 'normal' → string (default)
• 'list' → comma-separated list → string[]
• 'object' → JSON parsed object

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API

reactSubstitute(str, options)

import { reactSubstitute } from '@vojtechportes/react-substitute';

const result = reactSubstitute('...', options);

Return type:

• string (default)
• React.ReactNode when returnReactElement: true

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Options

• pattern?: RegExp
• modifierSeparator?: string
• contextSeparator?: string
• context?: unknown
• forceReplace?: boolean
• transform?: (value, placeholder, key, modifiers?, context?) => string | number
• contextType?: 'list' | 'normal' | 'object'
• returnReactElement?: boolean
• components?: any[]

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Example: React output with transform

import React, { PropsWithChildren } from 'react';
import { reactSubstitute } from '@vojtechportes/react-substitute';

type LinkProps = PropsWithChildren<{ to: string }>;
const Link: React.FC<LinkProps> = ({ to, children }) => (
  <a href={to}>{children}</a>
);

const text = 'Users: {user:123, John Doe}, {user:456, Jane Doe}';

const nodes = reactSubstitute(text, {
  contextType: 'list',
  context: { user: '' },

  transform: (_value, _placeholder, key, _modifiers, itemContext) => {
    if (key === 'user') {
      const [id, name] = itemContext as string[];
      return `<0 to="/users/${id}">${name}</0>`;
    }
    return '';
  },

  components: [<Link to="" />],
  returnReactElement: true,
});

Your transform() can output numeric tags like <0>...</0>. These are replaced by the corresponding element from components[].

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Development

yarn start
yarn build
yarn checkAll

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License

MIT