Inline process.browser for better code elimination (#2583)

packages/core/integration-tests/test/integration/process/index.js

@@ -0,0 +1,8 @@
+process.browser = false
+module.exports = function () {
+  return process.browser && test(process.browser);
+};
+
+function test(val) {
+  return val;
+}

packages/core/integration-tests/test/javascript.js

@@ -856,6 +856,45 @@ describe('javascript', function() {
     assert.equal(output, 'bartest');
   });
 
+  it('should replace process.browser on --target=browser', async function() {
+    let b = await bundle(
+      path.join(__dirname, '/integration/process/index.js'),
+      {
+        target: 'browser'
+      }
+    );
+
+    let output = await run(b);
+    assert.ok(output.toString().indexOf('process.browser') === -1);
+    assert.equal(output(), true);
+  });
+
+  it('should not replace process.browser on --target=node', async function() {
+    let b = await bundle(
+      path.join(__dirname, '/integration/process/index.js'),
+      {
+        target: 'node'
+      }
+    );
+
+    let output = await run(b);
+    assert.ok(output.toString().indexOf('process.browser') !== -1);
+    assert.equal(output(), false);
+  });
+
+  it('should not replace process.browser on --target=electron', async function() {
+    let b = await bundle(
+      path.join(__dirname, '/integration/process/index.js'),
+      {
+        target: 'electron'
+      }
+    );
+
+    let output = await run(b);
+    assert.ok(output.toString().indexOf('process.browser') !== -1);
+    assert.equal(output(), false);
+  });
+
   it('should support adding implicit dependencies', async function() {
     let b = await bundle(path.join(__dirname, '/integration/json/index.js'), {
       delegate: {

packages/core/parcel-bundler/src/assets/JSAsset.js

@@ -7,6 +7,7 @@ const babelParser = require('@babel/parser');
 const insertGlobals = require('../visitors/globals');
 const fsVisitor = require('../visitors/fs');
 const envVisitor = require('../visitors/env');
+const processVisitor = require('../visitors/process');
 const babel = require('../transforms/babel/transform');
 const babel7 = require('../transforms/babel/babel7');
 const generate = require('@babel/generator').default;
@@ -20,6 +21,7 @@ const isAccessedVarChanged = require('../utils/isAccessedVarChanged');
 
 const IMPORT_RE = /\b(?:import\b|export\b|require\s*\()/;
 const ENV_RE = /\b(?:process\.env)\b/;
+const BROWSER_RE = /\b(?:process\.browser)\b/;
 const GLOBAL_RE = /\b(?:process|__dirname|__filename|global|Buffer|define)\b/;
 const FS_RE = /\breadFileSync\b/;
 const SW_RE = /\bnavigator\s*\.\s*serviceWorker\s*\.\s*register\s*\(/;
@@ -155,6 +157,13 @@ class JSAsset extends Asset {
       await this.parseIfNeeded();
       this.traverseFast(envVisitor);
     }
+
+    // Inline process.browser
+    if (this.options.target === 'browser' && BROWSER_RE.test(this.contents)) {
+      await this.parseIfNeeded();
+      this.traverse(processVisitor);
+      this.isAstDirty = true;
+    }
   }
 
   async transform() {

packages/core/parcel-bundler/src/visitors/process.js

@@ -0,0 +1,17 @@
+const t = require('@babel/types');
+
+module.exports = {
+  MemberExpression(path) {
+    // Inline process.browser
+    const isProcess = path.node.object.name === 'process';
+    const isBrowser = path.node.property.name === 'browser';
+    const isAssignment = path.parentPath.type === 'AssignmentExpression';
+    if (isProcess && isBrowser) {
+      if (isAssignment) {
+        path.parentPath.remove();
+      } else {
+        path.replaceWith(t.booleanLiteral(true));
+      }
+    }
+  }
+};