package.json、scripts、dependenciesとdevDependencies

package.jsonの理由

フィールドの概要

// Emulate a minimal package.json as a JS object
const pkg = {
  name: "hello-app",
  version: "1.0.0",
  type: "module",
  scripts: {
    start: "node index.js",
    build: "echo building...",
    test: "echo tests..."
  },
  dependencies: {
    "chalk": "^5.3.0"
  },
  devDependencies: {
    "eslint": "^9.0.0"
  }
};

console.log("name:", pkg.name);
console.log("version:", pkg.version);
console.log("type:", pkg.type);
console.log("scripts:", Object.keys(pkg.scripts));

名前でスクリプトを実行

// Tiny emulator for "npm run <name>"
function runScript(name) {
  const cmd = pkg.scripts[name];
  if (!cmd) {
    console.log("no such script:", name);
    return;
  }
  console.log("running:", name, "->", cmd);
}

runScript("build");
runScript("test");
runScript("missing");

何をどこに置くか

// List production deps vs development-time tools
function listDeps() {
  console.log("deps:", Object.keys(pkg.dependencies));
  console.log("devDeps:", Object.keys(pkg.devDependencies));
}

// Rule of thumb in comments:
// dependencies -> needed at runtime (your app uses them when running)
// devDependencies -> only for development (lint, test, build tools)

listDeps();

Semverの基本

// Semantic version ranges (intent only)
// ^1.2.3  -> allow minor/patch updates (1.x compatible)
// ~1.2.3  -> allow patch updates (1.2.x)
// 1.2.3   -> exact version

const ranges = ["^1.2.3", "~1.2.3", "1.2.3"];
for (const r of ranges) {
  console.log("range:", r);
}

実践的なメモ

scriptsフィールドのクイズ

まとめ