install using "optionalDependencies"

lib/npm/node-install.ts

@@ -0,0 +1,77 @@
+import { pkgAndBinForCurrentPlatform } from './node-platform';
+
+import fs = require('fs');
+import os = require('os');
+import path = require('path');
+import child_process = require('child_process');
+
+declare const ESBUILD_VERSION: string;
+const toPath = path.join(__dirname, 'bin', 'esbuild');
+
+function validateBinaryVersion(...command: string[]): void {
+  command.push('--version');
+  const stdout = child_process.execFileSync(command.shift()!, command).toString().trim();
+  if (stdout !== ESBUILD_VERSION) {
+    throw new Error(`Expected ${JSON.stringify(ESBUILD_VERSION)} but got ${JSON.stringify(stdout)}`);
+  }
+}
+
+function isYarn2OrAbove(): boolean {
+  const { npm_config_user_agent } = process.env;
+  if (npm_config_user_agent) {
+    const match = npm_config_user_agent.match(/yarn\/(\d+)/);
+    if (match && match[1]) {
+      return parseInt(match[1], 10) >= 2;
+    }
+  }
+  return false;
+}
+
+// This feature was added to give external code a way to modify the binary
+// path without modifying the code itself. Do not remove this because
+// external code relies on this (in addition to esbuild's own test suite).
+if (process.env.ESBUILD_BINARY_PATH) {
+  // Patch the CLI use case (the "esbuild" command)
+  const pathString = JSON.stringify(process.env.ESBUILD_BINARY_PATH);
+  fs.writeFileSync(toPath, `#!/usr/bin/env node\n` +
+    `require('child_process').execFileSync(${pathString}, process.argv.slice(2), { stdio: 'inherit' });\n`);
+
+  // Patch the JS API use case (the "require('esbuild')" workflow)
+  const libMain = path.join(__dirname, 'lib', 'main.js');
+  const code = fs.readFileSync(libMain, 'utf8');
+  fs.writeFileSync(libMain, `var ESBUILD_BINARY_PATH = ${pathString};\n${code}`);
+
+  // Windows needs "node" before this command since it's a JavaScript file
+  validateBinaryVersion('node', toPath);
+}
+
+// This package contains a "bin/esbuild" JavaScript file that finds and runs
+// the appropriate binary executable. However, this means that running the
+// "esbuild" command runs another instance of "node" which is way slower than
+// just running the binary executable directly.
+//
+// Here we optimize for this by replacing the JavaScript file with the binary
+// executable at install time. This optimization does not work on Windows
+// because on Windows the binary executable must be called "esbuild.exe"
+// instead of "esbuild". This also doesn't work with Yarn 2+ because the Yarn
+// developers don't think binary modules should be used. See this thread for
+// details: https://github.com/yarnpkg/berry/issues/882. This optimization also
+// doesn't apply when npm's "--ignore-scripts" flag is used since in that case
+// this install script will not be run.
+else if (os.platform() !== 'win32' && !isYarn2OrAbove()) {
+  const { bin } = pkgAndBinForCurrentPlatform();
+  try {
+    fs.unlinkSync(toPath);
+    fs.linkSync(bin, toPath);
+  } catch (e) {
+    // Ignore errors here since this optimization is optional
+  }
+
+  // This is no longer a JavaScript file so don't run it using "node"
+  validateBinaryVersion(toPath);
+}
+
+else {
+  // Windows needs "node" before this command since it's a JavaScript file
+  validateBinaryVersion('node', toPath);
+}