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:

1import fs from 'node:fs';
2import detectIndent from 'detect-indent';
3
4/*
5{
6    "ilove": "pizza"
7}
8*/
9const file = fs.readFileSync('foo.json', 'utf8');
10
11// Tries to detect the indentation and falls back to a default if it can't
12const indent = detectIndent(file).indent || '    ';
13
14const json = JSON.parse(file);
15
16json.ilove = 'unicorns';
17
18fs.writeFileSync('foo.json', JSON.stringify(json, undefined, indent));
19/*
20{
21    "ilove": "unicorns"
22}
23*/

API

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

• amount {number} - Amount of indentation, for example 2
• type {'tab' | 'space' | undefined} - Type of indentation. Possible values are 'tab', 'space' or undefined if no indentation is detected
• indent {string} - Actual indentation

Algorithm

The current algorithm looks for the most common difference between two consecutive non-empty lines.

In the following example, even if the 4-space indentation is used 3 times whereas the 2-space one is used 2 times, it is detected as less used because there were only 2 differences with this value instead of 4 for the 2-space indentation:

1html {
2  box-sizing: border-box;
3}
4
5body {
6  background: gray;
7}
8
9p {
10    line-height: 1.3em;
11    margin-top: 1em;
12    text-indent: 2em;
13}

Source.

Furthermore, if there are more than one most used difference, the indentation with the most lines is selected.

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

1body {
2  background: gray;
3}
4
5p {
6    line-height: 1.3em;
7    margin-top: 1em;
8    text-indent: 2em;
9}

Related

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

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