JS: support different ECMAScript version to toggle optimizations, mer…

…ge with NoNullishOperator and add NoOptionalCatchParameter, fixes #540

cmd/minify/bash_completion

@@ -11,7 +11,7 @@ _minify_complete() {
     local cur prev flags mimes types
     cur="${COMP_WORDS[COMP_CWORD]}"
     prev="${COMP_WORDS[COMP_CWORD-1]}"
-    flags="-a --all --bundle --cpuprofile -l --list --match --memprofile --mime -o --output -p --preserve --preserve-links -r --recursive --type --url -v --verbose --version -w --watch --css-precision --html-keep-comments --html-keep-conditional-comments --html-keep-default-attrvals --html-keep-document-tags --html-keep-end-tags --html-keep-quotes --html-keep-whitespace --js-precision --js-keep-var-names --js-no-nullish-operator --json-precision --json-keep-numbers --svg-keep-comments --svg-precision -s --sync --xml-keep-whitespace"
+    flags="-a --all --bundle --cpuprofile -l --list --match --memprofile --mime -o --output -p --preserve --preserve-links -r --recursive --type --url -v --verbose --version -w --watch --css-precision --html-keep-comments --html-keep-conditional-comments --html-keep-default-attrvals --html-keep-document-tags --html-keep-end-tags --html-keep-quotes --html-keep-whitespace --js-precision --js-keep-var-names --js-version --json-precision --json-keep-numbers --svg-keep-comments --svg-precision -s --sync --xml-keep-whitespace"
     mimes="text/css text/html text/javascript application/javascript application/json image/svg+xml text/xml application/xml"
     types="css html js json svg xml"
 

cmd/minify/main.go

@@ -151,7 +151,7 @@ func run() int {
 	flag.BoolVar(&htmlMinifier.KeepQuotes, "html-keep-quotes", false, "Preserve quotes around attribute values")
 	flag.IntVar(&jsMinifier.Precision, "js-precision", 0, "Number of significant digits to preserve in numbers, 0 is all")
 	flag.BoolVar(&jsMinifier.KeepVarNames, "js-keep-var-names", false, "Preserve original variable names")
-	flag.BoolVar(&jsMinifier.NoNullishOperator, "js-no-nullish-operator", false, "Don't use the ?? nullish coalescing operator")
+	flag.IntVar(&jsMinifier.Version, "js-version", 0, "ECMAScript version to toggle supported optimizations (e.g. 2019, 2020), by default 0 is the latest version")
 	flag.IntVar(&jsonMinifier.Precision, "json-precision", 0, "Number of significant digits to preserve in numbers, 0 is all")
 	flag.BoolVar(&jsonMinifier.KeepNumbers, "json-keep-numbers", false, "Preserve original numbers instead of minifying them")
 	flag.BoolVar(&svgMinifier.KeepComments, "svg-keep-comments", false, "Preserve all comments")

js/js.go

@@ -10,6 +10,8 @@ import (
 	"github.com/tdewolff/parse/v2/js"
 )
 
+const esNext = 2022
+
 type blockType int
 
 const (
@@ -23,7 +25,8 @@ type Minifier struct {
 	Precision           int // number of significant digits
 	KeepVarNames        bool
 	useAlphabetVarNames bool
-	NoNullishOperator   bool
+	NoNullishOperator   bool // DEPRECATED, use version ES2020
+	Version             int
 }
 
 // Minify minifies JS data, it reads from r and writes to w.
@@ -33,6 +36,13 @@ func Minify(m *minify.M, w io.Writer, r io.Reader, params map[string]string) err
 
 // Minify minifies JS data, it reads from r and writes to w.
 func (o *Minifier) Minify(_ *minify.M, w io.Writer, r io.Reader, _ map[string]string) error {
+	if o.Version == 0 {
+		o.Version = esNext
+	}
+	if 2019 < o.Version && o.NoNullishOperator {
+		o.Version = 2019 // nullish operator was introduced in ES2020
+	}
+
 	z := parse.NewInput(r)
 	ast, err := js.Parse(z, js.Options{WhileToFor: true})
 	if err != nil {
@@ -303,7 +313,7 @@ func (m *jsMinifier) minifyStmt(i js.IStmt) {
 		if stmt.Catch != nil {
 			m.write(catchBytes)
 			stmt.Catch.List = optimizeStmtList(stmt.Catch.List, defaultBlock)
-			if v, ok := stmt.Binding.(*js.Var); ok && v.Uses == 1 {
+			if v, ok := stmt.Binding.(*js.Var); ok && v.Uses == 1 && 2019 <= m.o.Version {
 				stmt.Catch.Scope.Declared = stmt.Catch.Scope.Declared[1:]
 				stmt.Binding = nil
 			}

js/js_test.go

@@ -881,6 +881,37 @@ func TestJSVarRenaming(t *testing.T) {
 	}
 }
 
+func TestJSVersion(t *testing.T) {
+	versions := []int{esNext, 2020, 2019, 2018}
+
+	jsTests := []struct {
+		version int
+		js      string
+		before  string
+		after   string
+	}{
+		{2020, `a==null?b:a`, `a==null?b:a`, `a??b`},
+		{2019, `try{}catch(a){}`, `try{}catch(a){}`, `try{}catch{}`},
+	}
+
+	m := minify.New()
+	for _, tt := range jsTests {
+		for _, version := range versions {
+			t.Run(fmt.Sprintf("%d/%v", version, tt.js), func(t *testing.T) {
+				r := bytes.NewBufferString(tt.js)
+				w := &bytes.Buffer{}
+				o := Minifier{KeepVarNames: true, useAlphabetVarNames: true, Version: version}
+				err := o.Minify(m, w, r, nil)
+				if version < tt.version {
+					test.Minify(t, tt.js, err, w.String(), tt.before)
+				} else {
+					test.Minify(t, tt.js, err, w.String(), tt.after)
+				}
+			})
+		}
+	}
+}
+
 func TestReaderError(t *testing.T) {
 	r := test.NewErrorReader(0)
 	w := &bytes.Buffer{}

js/util.go

@@ -825,7 +825,7 @@ func (m *jsMinifier) optimizeCondExpr(expr *js.CondExpr, prec js.OpPrec) js.IExp
 	} else if isEqualExpr(expr.X, expr.Y) {
 		// if true and false bodies are equal
 		return groupExpr(&js.CommaExpr{[]js.IExpr{expr.Cond, expr.X}}, prec)
-	} else if nullishExpr, ok := toNullishExpr(expr); ok && !m.o.NoNullishOperator {
+	} else if nullishExpr, ok := toNullishExpr(expr); ok && 2020 <= m.o.Version {
 		// no need to check whether left/right need to add groups, as the space saving is always more
 		return nullishExpr
 	} else {