How to fix Import assignment cannot be used when targeting ECMAScript modules in TypeScript

// BEFORE - CommonJS import assignment (causes error)
import fs = require("fs");
import express = require("express");
import * as path from "path";  // This is actually ES module syntax

// AFTER - ES module syntax (correct for ES modules)
import fs from "fs";
import express from "express";
import * as path from "path";  // This is already correct

// For default exports:
import React from "react";
import lodash from "lodash";

// For named exports:
import { useState } from "react";
import { debounce } from "lodash";

// For namespace imports (already ES module syntax):
import * as fs from "fs";  // Alternative to default import

npx tsc
# or
npm run build

// tsconfig.json - For ES modules (modern projects)
{
  "compilerOptions": {
    "module": "es2022",  // or "esnext", "es2020", "es2015"
    "moduleResolution": "node16",  // or "bundler", "node"
    "target": "es2022",
    "esModuleInterop": true,
    "allowSyntheticDefaultImports": true
  }
}

// tsconfig.json - For CommonJS (Node.js compatibility)
{
  "compilerOptions": {
    "module": "commonjs",  // Allows import x = require()
    "moduleResolution": "node",
    "target": "es2022",
    "esModuleInterop": true
  }
}

// Library uses: export = MyClass
// In CommonJS projects:
import MyClass = require("old-library");

// In ES module projects, use esModuleInterop:
import MyClass from "old-library";
// Requires: "esModuleInterop": true in tsconfig.json

// Alternative: Use a namespace import
import * as OldLibrary from "old-library";
const MyClass = OldLibrary.default || OldLibrary;

{
  "compilerOptions": {
    "esModuleInterop": true,
    "allowSyntheticDefaultImports": true
  }
}

// package.json - For ES modules
{
  "type": "module",  // Tells Node.js to treat .js files as ES modules
  "exports": {
    ".": {
      "import": "./dist/index.js",
      "require": "./dist/index.cjs"
    }
  },
  "scripts": {
    "build": "tsc",
    "start": "node dist/index.js"
  }
}

{
  "type": "module",  // .js files are ES modules
  // .cjs files are CommonJS modules
}

// BEFORE - CommonJS conditional require (won't work in ES modules)
let module;
if (condition) {
  module = require("module-a");
} else {
  module = require("module-b");
}

// AFTER - ES module dynamic import
let module;
if (condition) {
  module = await import("module-a");
} else {
  module = await import("module-b");
}

// For synchronous-like behavior with top-level await:
const module = condition
  ? await import("module-a")
  : await import("module-b");

# 1. Update tsconfig.json
{
  "compilerOptions": {
    "module": "es2022",
    "moduleResolution": "node16"
  }
}

# 2. Update package.json
{
  "type": "module"
}

# 3. Convert all import statements
# Use a script or search/replace:
sed -i 's/import \(.*\) = require("\(.*\)")/import \1 from "\2"/g' src/**/*.ts

# 4. Update export statements
# Change:
# export = MyClass
# To:
# export default MyClass

# 5. Add .js extensions to relative imports (for Node16/NodeNext)
import { helper } from "./helper.js";  // Not "./helper"

# 6. Test thoroughly
npm run build
npm test