@babel/code-frame

What is @babel/code-frame?

The @babel/code-frame package is used to generate a string representing code with a specific error highlighted. It is often used to produce more readable error messages in development tools by showing the code snippet where an error has occurred along with line and column numbers.

What are @babel/code-frame's main functionalities?

Highlighting syntax errors in code

This feature allows developers to highlight syntax errors in their code. The code sample shows how to use the codeFrameColumns function to generate a string that highlights the location of an error in the source code.

const { codeFrameColumns } = require('@babel/code-frame');
const rawLines = `class Foo {
  constructor()
}
`;
const location = { start: { line: 2, column: 15 } };

const result = codeFrameColumns(rawLines, location, {
  highlightCode: true
});

console.log(result);

Other packages similar to @babel/code-frame

chalk

Chalk is a popular npm package for styling terminal strings. While it doesn't generate code frames, it can be used to colorize text and could be combined with other tools to highlight specific parts of code in the terminal.

cardinal

Cardinal is a syntax highlighter for JavaScript code that can be used in the terminal. It's similar to @babel/code-frame in that it can be used to make code more readable, but it focuses on syntax highlighting rather than pinpointing specific locations of errors.

highlight.js

Highlight.js is a syntax highlighter for the web. It supports many languages and can be used to highlight code blocks on web pages. Unlike @babel/code-frame, it is not specifically designed for highlighting error locations, but it can be used to enhance the readability of code snippets.

README

@babel/code-frame

Generate errors that contain a code frame that point to source locations.

Install

npm install --save-dev @babel/code-frame

Usage

import { codeFrameColumns } from '@babel/code-frame';

const rawLines = `class Foo {
  constructor()
}`;
const location = { start: { line: 2, column: 16 } };

const result = codeFrameColumns(rawLines, location, { /* options */ });

console.log(result);

  1 | class Foo {
> 2 |   constructor()
    |                ^
  3 | }

If the column number is not known, you may omit it.

You can also pass an end hash in location.

import { codeFrameColumns } from '@babel/code-frame';

const rawLines = `class Foo {
  constructor() {
    console.log("hello");
  }
}`;
const location = { start: { line: 2, column: 17 }, end: { line: 4, column: 3 } };

const result = codeFrameColumns(rawLines, location, { /* options */ });

console.log(result);

  1 | class Foo {
> 2 |   constructor() {
    |                 ^
> 3 |     console.log("hello");
    | ^^^^^^^^^^^^^^^^^^^^^^^^^
> 4 |   }
    | ^^^
  5 | };

Options

highlightCode

boolean, defaults to false.

Toggles syntax highlighting the code as JavaScript for terminals.

linesAbove

number, defaults to 2.

Adjust the number of lines to show above the error.

linesBelow

number, defaults to 3.

Adjust the number of lines to show below the error.

forceColor

boolean, defaults to false.

Enable this to forcibly syntax highlight the code as JavaScript (for non-terminals); overrides highlightCode.

message

string, otherwise nothing

Pass in a string to be displayed inline (if possible) next to the highlighted location in the code. If it can't be positioned inline, it will be placed above the code frame.

1 | class Foo {
> 2 |   constructor()
  |                ^ Missing {
3 | };

Upgrading from prior versions

Prior to version 7, the only API exposed by this module was for a single line and optional column pointer. The old API will now log a deprecation warning.

The new API takes a location object, similar to what is available in an AST.

This is an example of the deprecated (but still available) API:

import codeFrame from '@babel/code-frame';

const rawLines = `class Foo {
  constructor()
}`;
const lineNumber = 2;
const colNumber = 16;

const result = codeFrame(rawLines, lineNumber, colNumber, { /* options */ });

console.log(result);

To get the same highlighting using the new API:

import { codeFrameColumns } from '@babel/code-frame';

const rawLines = `class Foo {
  constructor() {
    console.log("hello");
  }
}`;
const location = { start: { line: 2, column: 16 } };

const result = codeFrameColumns(rawLines, location, { /* options */ });

console.log(result);