tessl/npm-prettier

Prettier is an opinionated code formatter that enforces consistent style across multiple languages including JavaScript, TypeScript, Flow, JSX, JSON, CSS, SCSS, Less, HTML, Vue, Angular, GraphQL, Markdown, and YAML.

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Utility Functions

Name: tessl/npm-prettier
Author: tessl

Prettier provides extensive utility functions for text processing, AST navigation, position tracking, and comment manipulation. These utilities are essential for plugin development and advanced formatting scenarios.

Importing Utilities

import { util } from 'prettier';

// Access all utilities
const { getStringWidth, skipWhitespace, addLeadingComment } = util;

String and Text Processing

getStringWidth

function getStringWidth(text: string): number

Get the display width of a string, accounting for Unicode characters, emoji, and ANSI escape codes.

Example:

const width1 = util.getStringWidth('hello'); // 5
const width2 = util.getStringWidth('你好');   // 4 (CJK characters are width 2)
const width3 = util.getStringWidth('🎉');    // 2 (emoji width)

getMaxContinuousCount

function getMaxContinuousCount(text: string, searchString: string): number

Count the maximum continuous occurrences of a substring in text.

Example:

const maxQuotes = util.getMaxContinuousCount('"""hello"""', '"'); // 3
const maxSpaces = util.getMaxContinuousCount('a    b  c', ' ');    // 4

getAlignmentSize

function getAlignmentSize(text: string, tabWidth: number, startIndex?: number): number

Calculate the alignment size for a text string, considering tabs and spaces.

Parameters:

text (string): Text to measure
tabWidth (number): Width of tab characters
startIndex (number, optional): Starting position (default: 0)

Example:

const size1 = util.getAlignmentSize('  text', 2);     // 2
const size2 = util.getAlignmentSize('\ttext', 4);     // 4
const size3 = util.getAlignmentSize(' \t text', 4);   // 5 (1 space + 4 tab - 1 for alignment)

getIndentSize

function getIndentSize(value: string, tabWidth: number): number

Calculate the indentation size of a string.

Example:

const indent1 = util.getIndentSize('    code', 2);  // 4
const indent2 = util.getIndentSize('\t\tcode', 4);  // 8
const indent3 = util.getIndentSize(' \t code', 4);  // 5

Quote Handling

makeString

function makeString(
  rawText: string, 
  enclosingQuote: "'" | '"', 
  unescapeUnnecessaryEscapes?: boolean
): string

Create a properly quoted and escaped string literal.

Parameters:

rawText (string): Raw text content
enclosingQuote (Quote): Quote character to use
unescapeUnnecessaryEscapes (boolean, optional): Remove unnecessary escapes

Example:

const quoted1 = util.makeString('hello "world"', "'"); // "'hello \"world\"'"
const quoted2 = util.makeString("it's nice", '"');     // '"it\'s nice"'
const quoted3 = util.makeString('simple', '"');        // '"simple"'

getPreferredQuote

function getPreferredQuote(
  text: string, 
  preferredQuoteOrPreferSingleQuote: "'" | '"' | boolean
): "'" | '"'

Determine the preferred quote character for a string to minimize escaping.

Parameters:

text (string): Text content to quote
preferredQuoteOrPreferSingleQuote (Quote | boolean): Preference setting

Example:

const quote1 = util.getPreferredQuote('hello "world"', "'"); // "'" (no escaping needed)
const quote2 = util.getPreferredQuote("it's nice", '"');     // '"' (no escaping needed)
const quote3 = util.getPreferredQuote('simple', true);       // "'" (prefer single)

Position and Navigation

Skip Functions

All skip functions follow this pattern:

Take text and startIndex parameters
Return new index position or false if pattern not found
Support optional backwards direction

interface SkipOptions {
  backwards?: boolean; // Skip in reverse direction
}

skipWhitespace

const skipWhitespace: (
  text: string, 
  startIndex: number | false, 
  options?: SkipOptions
) => number | false

Skip whitespace characters (spaces, tabs, newlines).

Example:

const text = 'code   \n  more';
const nextPos = util.skipWhitespace(text, 4); // 10 (after whitespace)
const prevPos = util.skipWhitespace(text, 10, { backwards: true }); // 4

skipSpaces

const skipSpaces: (
  text: string, 
  startIndex: number | false, 
  options?: SkipOptions
) => number | false

Skip space characters only (not tabs or newlines).

Example:

const text = 'code   \tmore';
const nextPos = util.skipSpaces(text, 4); // 7 (stops at tab)

skipNewline

function skipNewline(
  text: string, 
  startIndex: number | false, 
  options?: SkipOptions
): number | false

Skip a single newline character (LF, CRLF, or CR).

Example:

const text = 'line1\nline2';
const nextPos = util.skipNewline(text, 5); // 6 (after newline)

skipToLineEnd

const skipToLineEnd: (
  text: string, 
  startIndex: number | false, 
  options?: SkipOptions
) => number | false

Skip to the end of the current line.

skipEverythingButNewLine

const skipEverythingButNewLine: (
  text: string, 
  startIndex: number | false, 
  options?: SkipOptions
) => number | false

Skip all characters except newlines.

Generic skip Function

function skip(characters: string | RegExp): (
  text: string, 
  startIndex: number | false, 
  options?: SkipOptions
) => number | false

Create a custom skip function for specific characters or patterns.

Example:

const skipDigits = util.skip(/\d/);
const skipPunctuation = util.skip('.,;:!?');

const text = '123abc';
const afterDigits = skipDigits(text, 0); // 3

const text2 = '...text';
const afterPuncts = skipPunctuation(text2, 0); // 3

Comment Processing

skipInlineComment

function skipInlineComment(text: string, startIndex: number | false): number | false

Skip JavaScript-style inline comments (// comment).

Example:

const text = 'code // comment\nmore';
const afterComment = util.skipInlineComment(text, 5); // 15 (after comment)

skipTrailingComment

function skipTrailingComment(text: string, startIndex: number | false): number | false

Skip JavaScript-style block comments (/* comment */).

Example:

const text = 'code /* comment */ more';
const afterComment = util.skipTrailingComment(text, 5); // 18 (after comment)

Character and Position Testing

hasNewline

function hasNewline(text: string, startIndex: number, options?: SkipOptions): boolean

Check if there's a newline at the specified position.

Example:

const text = 'line1\nline2';
const hasNL = util.hasNewline(text, 5); // true

hasNewlineInRange

function hasNewlineInRange(text: string, startIndex: number, endIndex: number): boolean

Check if there's a newline within a character range.

Example:

const text = 'no newline here';
const hasNL = util.hasNewlineInRange(text, 0, 10); // false

hasSpaces

function hasSpaces(text: string, startIndex: number, options?: SkipOptions): boolean

Check if there are spaces at the specified position.

getNextNonSpaceNonCommentCharacterIndex

function getNextNonSpaceNonCommentCharacterIndex(text: string, startIndex: number): number | false

Find the index of the next significant character, skipping whitespace and comments.

Example:

const text = 'code  /* comment */  more';
const nextChar = util.getNextNonSpaceNonCommentCharacterIndex(text, 4); // 20 ('m' in 'more')

getNextNonSpaceNonCommentCharacter

function getNextNonSpaceNonCommentCharacter(text: string, startIndex: number): string

Get the next significant character, skipping whitespace and comments.

Example:

const text = 'code  /* comment */  more';
const nextChar = util.getNextNonSpaceNonCommentCharacter(text, 4); // 'm'

isNextLineEmpty

function isNextLineEmpty(text: string, startIndex: number): boolean

Check if the next line after the given position is empty.

Example:

const text = 'line1\n\nline3';
const isEmpty = util.isNextLineEmpty(text, 5); // true (line after line1 is empty)

isPreviousLineEmpty

function isPreviousLineEmpty(text: string, startIndex: number): boolean

Check if the previous line before the given position is empty.

Example:

const text = 'line1\n\nline3';
const isEmpty = util.isPreviousLineEmpty(text, 8); // true (line before line3 is empty)

Comment Manipulation

addLeadingComment

function addLeadingComment(node: any, comment: any): void

Add a comment before an AST node.

Example:

const node = { type: 'Identifier', name: 'x' };
const comment = { type: 'Line', value: ' This is x' };
util.addLeadingComment(node, comment);
// node.leadingComments = [comment]

addTrailingComment

function addTrailingComment(node: any, comment: any): void

Add a comment after an AST node.

Example:

const node = { type: 'Identifier', name: 'x' };
const comment = { type: 'Line', value: ' End of x' };
util.addTrailingComment(node, comment);
// node.trailingComments = [comment]

addDanglingComment

function addDanglingComment(node: any, comment: any, marker: any): void

Add a comment inside an AST node (not leading or trailing).

Parameters:

node (any): AST node to add comment to
comment (any): Comment object to add
marker (any): Marker for comment placement

Example:

const node = { type: 'ObjectExpression', properties: [] };
const comment = { type: 'Block', value: ' empty object ' };
util.addDanglingComment(node, comment, 'inside');
// node.comments = [comment]

Usage Patterns

Text Processing Pipeline

function processText(text, startIndex) {
  // Skip initial whitespace
  let pos = util.skipWhitespace(text, startIndex);
  if (pos === false) return null;
  
  // Skip comments
  pos = util.skipInlineComment(text, pos) || pos;
  pos = util.skipTrailingComment(text, pos) || pos;
  
  // Get next significant character
  const nextChar = util.getNextNonSpaceNonCommentCharacter(text, pos);
  
  return {
    position: pos,
    character: nextChar,
    width: util.getStringWidth(text.slice(startIndex, pos))
  };
}

String Quoting Logic

function smartQuote(text, preferSingle = false) {
  const preferred = preferSingle ? "'" : '"';
  const optimal = util.getPreferredQuote(text, preferred);
  return util.makeString(text, optimal, true);
}

Position Navigation

function findStatementEnd(text, startIndex) {
  let pos = startIndex;
  
  while (pos < text.length) {
    // Skip whitespace and comments
    pos = util.skipWhitespace(text, pos) || pos;
    pos = util.skipInlineComment(text, pos) || pos;
    pos = util.skipTrailingComment(text, pos) || pos;
    
    // Check for statement terminator
    if (text[pos] === ';' || util.hasNewline(text, pos)) {
      return pos;
    }
    
    pos++;
  }
  
  return pos;
}

Comment Processing

function attachComments(ast, comments) {
  for (const comment of comments) {
    const beforeNode = findNodeBefore(ast, comment.start);
    const afterNode = findNodeAfter(ast, comment.end);
    
    if (beforeNode && isOnSameLine(beforeNode.end, comment.start)) {
      util.addTrailingComment(beforeNode, comment);
    } else if (afterNode && isOnSameLine(comment.end, afterNode.start)) {
      util.addLeadingComment(afterNode, comment);
    } else {
      // Dangling comment
      const parentNode = findParentNode(ast, comment);
      if (parentNode) {
        util.addDanglingComment(parentNode, comment, 'inside');
      }
    }
  }
}

Indentation Calculation

function calculateIndentation(line, tabWidth) {
  const trimmed = line.trimStart();
  const indentText = line.slice(0, line.length - trimmed.length);
  
  return {
    size: util.getIndentSize(indentText, tabWidth),
    alignment: util.getAlignmentSize(indentText, tabWidth),
    text: indentText,
    content: trimmed
  };
}

Deprecated Functions

isNextLineEmptyAfterIndex (Deprecated)

function isNextLineEmptyAfterIndex(text: string, startIndex: number): boolean

⚠️ Deprecated: This function will be removed in v4. Use isNextLineEmpty instead.

Legacy function that checks if the next line after the given index is empty.

Example:

// Deprecated usage
const isEmpty = util.isNextLineEmptyAfterIndex(text, 5);

// Modern equivalent
const isEmpty = util.isNextLineEmpty(text, 5);

Performance Notes

Skip functions return early with false if startIndex is false
String width calculation caches results for repeated calls
Comment utilities modify AST nodes in place
Position functions work with zero-based indices
All functions handle edge cases (empty strings, invalid positions)

Install with Tessl CLI

npx tessl i tessl/npm-prettier

docs

plugin-development.md

utilities.md

tile.json

tessl/npm-prettier

utilities.md.css-3qkkll{font-size:var(--chakra-font-sizes-sm);font-weight:var(--chakra-font-weights-normal);color:var(--chakra-colors-gray-300);}docs/

Utility Functions

Importing Utilities

String and Text Processing

getStringWidth

getMaxContinuousCount

getAlignmentSize

getIndentSize

Quote Handling

makeString

getPreferredQuote

Position and Navigation

Skip Functions

skipWhitespace

skipSpaces

skipNewline

skipToLineEnd

skipEverythingButNewLine

Generic skip Function

Comment Processing

skipInlineComment

skipTrailingComment

Character and Position Testing

hasNewline

hasNewlineInRange

hasSpaces

getNextNonSpaceNonCommentCharacterIndex

getNextNonSpaceNonCommentCharacter

isNextLineEmpty

isPreviousLineEmpty

Comment Manipulation

addLeadingComment

addTrailingComment

addDanglingComment

Usage Patterns

Text Processing Pipeline

String Quoting Logic

Position Navigation

Comment Processing

Indentation Calculation

Deprecated Functions

isNextLineEmptyAfterIndex (Deprecated)

Performance Notes

utilities.mddocs/