detect-indent

Detect the indentation of code

Pass in a string of any kind of text and get the indentation.

Use cases

• Persisting the indentation when modifying a file.
• Have new content match the existing indentation.
• Setting the right indentation in your editor.

Install

npm install detect-indent

Usage

Here we modify a JSON file while persisting the indentation:

import fs from 'node:fs';
import detectIndent from 'detect-indent';

/*
{
    "ilove": "pizza"
}
*/
const file = fs.readFileSync('foo.json', 'utf8');

// Tries to detect the indentation and falls back to a default if it can't
const indent = detectIndent(file).indent || '    ';

const json = JSON.parse(file);

json.ilove = 'unicorns';

fs.writeFileSync('foo.json', JSON.stringify(json, undefined, indent));
/*
{
    "ilove": "unicorns"
}
*/

API

Accepts a string and returns an object with stats about the indentation:

• type {'tab' | 'space' | undefined} - The type of indentation. It is undefined if no indentation is detected.
• amount {number} - The amount of indentation. For example, 2.
• indent {string} - The actual indentation.

Algorithm

The current algorithm looks for the most common difference between two consecutive non-empty lines. Single-space indentations and changes are ignored by default to prevent common false positives from comment alignment.

In the following example, even if 4-space indentation appears 3 times while 2-space appears only 2 times, the 2-space indentation is detected because there are 4 indent changes of 2 spaces vs only 2 changes of 4 spaces:

html {
  box-sizing: border-box;
}

body {
  background: gray;
}

p {
    line-height: 1.3em;
    margin-top: 1em;
    text-indent: 2em;
}

Source.

Furthermore, if there are multiple indent differences with the same usage count, the indentation with the most lines is selected.

In the following example, the indentation is detected as 4-spaces:

body {
  background: gray;
}

p {
    line-height: 1.3em;
    margin-top: 1em;
    text-indent: 2em;
}

Related

• detect-indent-cli - CLI for this module
• detect-newline - Detect the dominant newline character of a string
• detect-indent-rs - Rust port
• detect-indent-py - Python port