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@babel/code-frame

Install​

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

Usage​

codeFrameColumns​

The codeFrameColumns function allows you to decorate a code snipped with line numbers and with a marker pointing to a specific location.

It will also optionally highlight your code, defaulting to what is supported by the output terminal.

JavaScript
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.

JavaScript
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 | };

highlight​

The highlight function adds syntax highlighting to a code snipped, to be displayed in a terminal.

JavaScript
import { highlight } from "@babel/code-frame";

const code = `class Foo {
  constructor()
}`;

const result = highlight(code);

console.log(result);
JavaScript
class Foo {
  constructor()
}

Migrating from @babel/highlight​

The highlight functionality was originally split in its own package, @babel/highlight.

You can migrate as follows:

Using @babel/highlightUsing @babel/code-frame
JavaScript
import highlight from "@babel/highlight";

highlight(text, { forceColor: true });
JavaScript
import { highlight } from "@babel/code-frame";

highlight(text);
JavaScript
import highlight from "@babel/highlight";

highlight(text);
JavaScript
import { highlight } from "@babel/code-frame";

process.stdout.hasColors() ? highlight(text) : text;

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:

JavaScript
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:

JavaScript
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);