install using "optionalDependencies"

lib/npm/node-install.ts

@@ -0,0 +1,53 @@
+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(binaryPath: string): void {
+  const stdout = child_process.execFileSync(binaryPath, ['--version']).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 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.
+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
+  }
+}
+
+// Verify that the binary is the correct version
+validateBinaryVersion(toPath);