Custom Element and Web Component

Oct 13, 2025 by wbrum.org 103 views

BLink Cannot Read Properties of Null (Reading 'config')

When working with complex web applications, it's not uncommon to encounter unexpected errors. In this case, we're dealing with a peculiar issue involving the BLink component from the Bootstrap Vue library. The error message Cannot read properties of null (reading 'config') is quite cryptic, but we'll break it down and explore possible solutions.

To provide context, we're using the BDropdown component, which is a part of the Bootstrap Vue library. This component is configured with BDropdownItems that have href props, one for each row in a grid managed by the popular Datatables library. The grid is wrapped in a custom element using Vue's web component tools.

The error occurs in the setup function of BLink when it calls useBLinkTagResolver. Specifically, the issue arises when appContext.app.config is null. This might seem like a straightforward null check scenario, but there's more to it.

Custom Element and Web Component

It's worth noting that the BDropdown is wrapped in a custom element using Vue's web component tools. This might be relevant to the issue, as custom elements can behave differently than standard HTML elements.

Datatable Paging Controls

The error occurs when the user uses the Datatable paging controls to page view "page 2" of the grid data and then pages back to "page 1." This suggests that the Datatable is reusing DOM elements and just updating their attributes. The href properties of the BDropdownItems are bound to props so that the grid can update the href targets - each BDropdown has hrefs specific to data of each row.

Based on the information provided, here are some possible causes for the error:

Null check: The error message suggests that appContext.app.config is null. This could be due to a null check issue or a missing configuration.
Custom element behavior: The custom element wrapper might be causing the issue. Web components can behave differently than standard HTML elements, and this might be contributing to the error.
Datatable reusing DOM elements: The Datatable's behavior of reusing DOM elements and updating their attributes might be causing the issue. This could lead to unexpected behavior and errors.

To troubleshoot this issue, we can follow these steps:

Verify configuration: Ensure that the appContext.app.config is properly configured and not null.
Check custom element behavior: Investigate the custom element wrapper and its behavior to see if it's causing the issue.
Inspect Datatable behavior: Examine the Datatable's behavior and see if it's reusing DOM elements and updating their attributes correctly.
Use debugging tools: Utilize debugging tools like the browser's developer tools or a debugging library to inspect the component's behavior and identify the root cause of the issue.

The BLink Cannot read properties of null (reading 'config') error is a complex issue that requires a thorough investigation. By understanding the background information, custom element behavior, and Datatable's behavior, we can identify possible causes and troubleshoot the issue. By following the troubleshooting steps, we can resolve the error and ensure that our application works as expected.

For further information on the Bootstrap Vue library, custom elements, and web components, you can refer to the following resources:

Here are some code snippets that might be relevant to the issue:

// useBLinkTagResolver function
import { useBLinkTagResolver } from 'bootstrap-vue-next/src/composables/useBLinkHelper';

// BDropdown component
<template>
  <b-dropdown>
    <b-dropdown-item href="{{ item.href }}">{{ item.text }}</b-dropdown-item>
  </b-dropdown>
</template>

<script>
export default {
  props: {
    item: {
      type: Object,
      required: true
    }
  }
}
</script>

// Datatable component
<template>
  <table>
    <thead>
      <tr>
        <th>Column 1</th>
        <th>Column 2</th>
      </tr>
    </thead>
    <tbody>
      <tr v-for="item in items" :key="item.id">
        <td>{{ item.column1 }}</td>
        <td>{{ item.column2 }}</td>
      </tr>
    </tbody>
  </table>
</template>

<script>
export default {
  data() {
    return {
      items: []
    }
  },
  mounted() {
    this.$axios.get('/api/items')
      .then(response => {
        this.items = response.data;
      })
      .catch(error => {
        console.error(error);
      });
  }
}
</script>

Note that these code snippets are for illustration purposes only and might not be directly related to the issue at hand.
BLink Cannot Read Properties of Null (Reading 'config') Q&A

In our previous article, we explored the issue of BLink Cannot read properties of null (reading 'config') and its possible causes. In this Q&A article, we'll address some common questions related to this issue and provide additional insights to help you troubleshoot and resolve the problem.

Q: What is the root cause of the BLink Cannot read properties of null (reading 'config') error?

A: The root cause of the error is likely due to a null check issue or a missing configuration in the appContext.app.config object. This could be caused by a custom element wrapper, a web component, or the Datatable's behavior of reusing DOM elements and updating their attributes.

Q: How can I troubleshoot the issue?

A: To troubleshoot the issue, you can follow these steps:

Verify configuration: Ensure that the appContext.app.config is properly configured and not null.
Check custom element behavior: Investigate the custom element wrapper and its behavior to see if it's causing the issue.
Inspect Datatable behavior: Examine the Datatable's behavior and see if it's reusing DOM elements and updating their attributes correctly.
Use debugging tools: Utilize debugging tools like the browser's developer tools or a debugging library to inspect the component's behavior and identify the root cause of the issue.

Q: What are some common mistakes that can lead to this error?

A: Some common mistakes that can lead to this error include:

Missing configuration: Failing to configure the appContext.app.config object properly.
Custom element wrapper issues: Using a custom element wrapper that causes the issue.
Datatable behavior issues: The Datatable's behavior of reusing DOM elements and updating their attributes causing the issue.

Q: How can I prevent this error from occurring in the future?

A: To prevent this error from occurring in the future, you can:

Verify configuration: Ensure that the appContext.app.config is properly configured and not null.
Use debugging tools: Utilize debugging tools like the browser's developer tools or a debugging library to inspect the component's behavior and identify potential issues.
Test thoroughly: Test your application thoroughly to ensure that it works as expected.

Q: What are some additional resources that can help me troubleshoot this issue?

A: Some additional resources that can help you troubleshoot this issue include:

Q: Can you provide some code snippets that might be relevant to the issue?

A: Here are some code snippets that might be relevant to the issue:

// useBLinkTagResolver function
import { useBLinkTagResolver } from 'bootstrap-vue-next/src/composables/useBLinkHelper';

// BDropdown component
<template>
  <b-dropdown>
    <b-dropdown-item href="{{ item.href }}">{{ item.text }}</b-dropdown-item>
  </b-dropdown>
</template>

<script>
export default {
  props: {
    item: {
      type: Object,
      required: true
    }
  }
}
</script>

// Datatable component
<template>
  <table>
    <thead>
      <tr>
        <th>Column 1</th>
        <th>Column 2</th>
      </tr>
    </thead>
    <tbody>
      <tr v-for="item in items" :key="item.id">
        <td>{{ item.column1 }}</td>
        <td>{{ item.column2 }}</td>
      </tr>
    </tbody>
  </table>
</template>

<script>
export default {
  data() {
    return {
      items: []
    }
  },
  mounted() {
    this.$axios.get('/api/items')
      .then(response => {
        this.items = response.data;
      })
      .catch(error => {
        console.error(error);
      });
  }
}
</script>

Note that these code snippets are for illustration purposes only and might not be directly related to the issue at hand.

The BLink Cannot read properties of null (reading 'config') error is a complex issue that requires a thorough investigation. By understanding the possible causes, troubleshooting steps, and additional resources, you can identify the root cause of the issue and resolve the problem. Remember to verify configuration, check custom element behavior, inspect Datatable behavior, and use debugging tools to troubleshoot the issue.