Cannot read properties of undefined (reading ‘length’)

Explanation of the problem

function mapFromLineView(lineView, line, lineN) {
    if (lineView.line == line) {
        return {map: lineView.measure.map, cache: lineView.measure.cache};
    }
    for (var i = 0; i < lineView.rest.length; i++) {
        if (lineView.rest[i] == line) {
            return {map: lineView.measure.maps[i], cache: lineView.measure.caches[i]};
        }
    }
    for (var i$1 = 0; i$1 < lineView.rest.length; i$1++) {
        if (lineNo(lineView.rest[i$1]) > lineN) {
            return {map: lineView.measure.maps[i$1], cache: lineView.measure.caches[i$1], before: true};
        }
    }
}

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Problem solution for Cannot read properties of undefined (reading ‘length’)

function mapFromLineView(lineView, line, lineN) {
    if (lineView.line == line) {
        return {map: lineView.measure.map, cache: lineView.measure.cache};
    }
    if (lineView.rest && lineView.rest.length) {
        for (var i = 0; i < lineView.rest.length; i++) {
            if (lineView.rest[i] == line) {
                return {map: lineView.measure.maps[i], cache: lineView.measure.caches[i]};
            }
        }
    }
    for (var i$1 = 0; i$1 < lineView.rest.length; i$1++) {
        if (lineNo(lineView.rest[i$1]) > lineN) {
            return {map: lineView.measure.maps[i$1], cache: lineView.measure.caches[i$1], before: true};
        }
    }
}

Other popular problems with JedWatson React Codemirror

Problem: ReferenceError: “navigator” is not defined

This error occurs when trying to import and render the ‘JedWatson React Codemirror’ component. It is because ‘navigator’ is not defined in the Node environment, but it is available in the browser environment.

Solution:

let CodeMirror = null;
if (typeof window !== 'undefined' && typeof window.navigator !== 'undefined') {
  CodeMirror = require('react-codemirror');
  require('codemirror/mode/yaml/yaml');
  require('codemirror/mode/dockerfile/dockerfile');
}

And then render the component with the condition:

// render
   { CodeMirror && <CodeMirror ... /> }

Problem: Compatibility issues with NextJS

When using NextJS, server-side rendering (SSR) can cause issues with the ‘JedWatson React Codemirror’ component. This is because the component relies on certain browser APIs that are not available in the Node environment.

Solution:

The solution is to use the ‘dynamic’ component provided by NextJS and set the ‘ssr’ property to ‘false’:

import dynamic from 'next/dynamic'; 
const CodeMirror = dynamic(() => import('react-codemirror'), { ssr: false });

Problem: Inefficient Rendering

In some cases, the ‘JedWatson React Codemirror’ component can cause slow rendering times, especially when dealing with large amounts of code or data. This can negatively impact the performance of the entire application.

Solution:

The solution is to optimize the rendering process by using the ‘shouldComponentUpdate’ lifecycle method to avoid unnecessary renderings and only render when there are actual changes to the component’s state. Additionally, the ‘key’ property can be used to ensure that the component only re-renders when the code or data changes:

class CodeEditor extends React.Component {
  shouldComponentUpdate(nextProps) {
    return nextProps.value !== this.props.value;
  }

  render() {
    return (
      <CodeMirror
        key={this.props.value}
        value={this.props.value}
        onChange={this.props.onChange}
      />
    );
  }
}

A brief introduction to JedWatson React Codemirror

JedWatson React Codemirror is a library that provides a React component for using the CodeMirror code editor in React applications. The library allows developers to easily integrate a feature-rich code editor into their projects without having to worry about managing the complexities of the underlying CodeMirror library.

The library provides a number of useful features for the code editor, such as syntax highlighting, line numbering, and the ability to set custom themes. It also supports a number of customization options that allow developers to modify the behavior and appearance of the editor to suit their needs. This includes options for controlling the size and position of the editor, as well as support for adding custom keybindings and customizing the context menu.

Most popular use cases for JedWatson React Codemirror

1. Text Editing: JedWatson React Codemirror provides a text editing component for web applications, allowing users to create and edit source code, rich text, and other text-based content with syntax highlighting, line numbering, and more.
2. Code Highlighting: The component supports a wide range of programming languages, providing accurate syntax highlighting for each language. This can be seen in the code block below where JavaScript code is rendered with syntax highlighting in the Codemirror component:

import React, { useState } from "react";
import Codemirror from "react-codemirror";

const App = () => {
  const [code, setCode] = useState("// type your code here");
  return (
    <Codemirror
      value={code}
      onChange={setCode}
      options={{
        mode: "javascript",
        lineNumbers: true,
      }}
    />
  );
};

export default App;