Regular Expressions 101

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An explanation of your regex will be automatically generated as you type.
Detailed match information will be displayed here automatically.
  • All Tokens
  • Common Tokens
  • General Tokens
  • Anchors
  • Meta Sequences
  • Quantifiers
  • Group Constructs
  • Character Classes
  • Flags/Modifiers
  • Substitution
  • A single character of: a, b or c
    [abc]
  • A character except: a, b or c
    [^abc]
  • A character in the range: a-z
    [a-z]
  • A character not in the range: a-z
    [^a-z]
  • A character in the range: a-z or A-Z
    [a-zA-Z]
  • Any single character
    .
  • Alternate - match either a or b
    a|b
  • Any whitespace character
    \s
  • Any non-whitespace character
    \S
  • Any digit
    \d
  • Any non-digit
    \D
  • Any word character
    \w
  • Any non-word character
    \W
  • Non-capturing group
    (?:...)
  • Capturing group
    (...)
  • Zero or one of a
    a?
  • Zero or more of a
    a*
  • One or more of a
    a+
  • Exactly 3 of a
    a{3}
  • 3 or more of a
    a{3,}
  • Between 3 and 6 of a
    a{3,6}
  • Start of string
    ^
  • End of string
    $
  • A word boundary
    \b
  • Non-word boundary
    \B

Regular Expression
No Match

/
/
g

Test String

Code Generator

Generated Code

const regex = /(?<=^|[\n;](?:[\t ]*(?:\w+ )?)?)import\s*(?<type>type(?=\s+))?(?:[\s"']*(?<imports>[\w\t\n\r "$'*,/{}-]+?)\s+from\s*)?["']\s*(?<specifier>(?:(?<='\s*)[^']*[^\s'](?=\s*'))|(?:(?<="\s*)[^"]*[^\s"](?=\s*")))\s*["'](?:\s+assert\s+(?<assertion>{[\w\t\n\r "':]+?}))?(?=[\s;]*)/g; // Alternative syntax using RegExp constructor // const regex = new RegExp('(?<=^|[\\n;](?:[\\t ]*(?:\\w+ )?)?)import\\s*(?<type>type(?=\\s+))?(?:[\\s"\']*(?<imports>[\\w\\t\\n\\r "$\'*,\/{}-]+?)\\s+from\\s*)?["\']\\s*(?<specifier>(?:(?<=\'\\s*)[^\']*[^\\s\'](?=\\s*\'))|(?:(?<="\\s*)[^"]*[^\\s"](?=\\s*")))\\s*["\'](?:\\s+assert\\s+(?<assertion>{[\\w\\t\\n\\r "\':]+?}))?(?=[\\s;]*)', 'g') const str = `/** * @file Interfaces * @module mlly/interfaces */ export type { default as DynamicImport } from './import-dynamic' export type { default as StaticImport } from './import-static' export type { default as ResolveOptions } from './options-resolve' export type { default as ResolveAliasOptions } from './options-resolve-alias' export type { default as Statement } from './statement' export type { default as ExportStatement } from './statement-export' export type { default as ImportStatement } from './statement-import' export type { default as RequireStatement } from './statement-require' import { CONDITIONS, RESOLVE_EXTENSIONS } from '#src/constants' import type { ResolveOptions } from '#src/interfaces' import type { SpecifierType } from '#src/types' import isBuiltin from '@flex-development/is-builtin' import { moduleResolve, type ErrnoException } from 'import-meta-resolve' import { pathToFileURL, URL } from 'node:url' import upath from 'upath' import toBareSpecifier from './to-bare-specifier' import toRelativeSpecifier from './to-relative-specifier' import 'file:///home/dir/file.ts' import pkg from './package.json' assert { type:'json' } import * as color from 'colorette' import consola from 'consola' import { defu } from 'defu' import type { Format } from 'esbuild' import fse from 'fs-extra' import * as pathe from 'pathe' import { resolve } from 'node:path' import url from 'node:url' import type { PackageJson } from 'pkg-types' import pb from 'pretty-bytes' import { EXT_DTS_REGEX, IGNORE_PATTERNS } from './config/constants' import loadBuildConfig from './config/load' import type { Config, Entry, Result } from './interfaces' import type { OutputExtension } from './types' import { readPackage, type PackageJson } from "read-pkg" import {OutputExtension} from './types' import analyzeResults from './utils/analyze-results' import esbuilder from './utils/esbuilder'; import write from './utils/write';import write2 from './utils/write' // import write from './utils/write' import 'side-effect.mjs' import type StatementType from '../types/statement-type' import type { BuildOptions, BuildResult, OutputFile, Plugin, PluginBuild } from './esbuild' import defaultExport from "module-name"; import * as name from "module-name"; import { export1 } from "module-name"; import { export1 as alias1 } from "module-name"; import { default as alias } from "module-name"; import { export1, export2 } from "module-name"; import { export1, export2 as alias2 } from "module-name"; import { 'string name' as alias } from "module-name"; import { "string name" as alias } from "module-name"; import defaultExport, { export1 } from "module-name"; import defaultExport, * as name from "module-name"; import "module-name"; import 'module-name'; import './polyfill.mjs' import { "h-i" as hi } from './hi.js' import { 'j-k' as jk } from "./jk.js" declare module '__fixtures__/values' { import MAX_VALUE from '#fixtures/max-value' import MIN_VALUE from '#fixtures/min-value' } const ERR_UNSUPPORTED_DIR_IMPORT: NodeErrorConstructor< ErrorConstructor, [string, string] > = createNodeError( ErrorCode.ERR_UNSUPPORTED_DIR_IMPORT, Error, 'Directory import '%s' is not supported resolving ES modules imported from %s' ) const text: string = await resolveModules(output.text, { conditions: [format === 'esm' ? 'import' : 'require'], ext: ext as Ext, extensions, parent }) /** * @example * import write from './utils/write' * write() */ import { 'j-k' as jk } from "./jk.js"`; // Reset `lastIndex` if this regex is defined globally // regex.lastIndex = 0; let m; while ((m = regex.exec(str)) !== null) { // This is necessary to avoid infinite loops with zero-width matches if (m.index === regex.lastIndex) { regex.lastIndex++; } // The result can be accessed through the `m`-variable. m.forEach((match, groupIndex) => { console.log(`Found match, group ${groupIndex}: ${match}`); }); }

Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for JavaScript, please visit: https://developer.mozilla.org/en/docs/Web/JavaScript/Guide/Regular_Expressions