vant/packages/vant-cli/src/compiler/get-deps.ts

import { join } from 'path';
import { SCRIPT_EXTS } from '../common/constant';
import { readFileSync, existsSync } from 'fs-extra';

let depsMap: Record<string, string[]> = {};
let existsCache: Record<string, boolean> = {};

// https://regexr.com/47jlq
const IMPORT_RE = /import\s+?(?:(?:(?:[\w*\s{},]*)\s+from\s+?)|)(?:(?:".*?")|(?:'.*?'))[\s]*?(?:;|$|)/g;

function matchImports(code: string): string[] {
  return code.match(IMPORT_RE) || [];
}

function exists(filePath: string) {
  if (!(filePath in existsCache)) {
    existsCache[filePath] = existsSync(filePath);
  }

  return existsCache[filePath];
}

export function fillExt(filePath: string) {
  for (let i = 0; i < SCRIPT_EXTS.length; i++) {
    const completePath = `${filePath}${SCRIPT_EXTS[i]}`;
    if (exists(completePath)) {
      return completePath;
    }
  }

  for (let i = 0; i < SCRIPT_EXTS.length; i++) {
    const completePath = `${filePath}/index${SCRIPT_EXTS[i]}`;
    if (exists(completePath)) {
      return completePath;
    }
  }

  return '';
}

function getPathByImport(code: string, filePath: string) {
  const divider = code.includes('"') ? '"' : "'";
  const relativePath = code.split(divider)[1];

  if (relativePath.includes('.')) {
    return fillExt(join(filePath, '..', relativePath));
  }

  return null;
}

export function clearDepsCache() {
  depsMap = {};
  existsCache = {};
}

export function getDeps(filePath: string) {
  if (depsMap[filePath]) {
    return depsMap[filePath];
  }

  const code = readFileSync(filePath, 'utf-8');
  const imports = matchImports(code);
  const paths = imports
    .map(item => getPathByImport(item, filePath))
    .filter(item => !!item) as string[];

  depsMap[filePath] = paths;

  paths.forEach(getDeps);

  return paths;
}