JS: better compression of if/else statements with return/throw

js/js_test.go

@@ -260,6 +260,7 @@ func TestJS(t *testing.T) {
 		{`if(a,b)b;else d`, `a,b||d`},
 		{`if(a=b)a;else b`, `(a=b)||b`},
 		{`if(!a&&!b){return true}else if(!a||!b){return false}return c&&d`, `return!a&&!b||!(!a||!b)&&c&&d`},
+		{`if(!a){if(b){throw c}else{return c}}else{return a}`, `if(a)return a;if(b)throw c;return c`},
 
 		// var declarations
 		{`var a;var b;a,b`, `var a,b;a,b`},

js/stmtlist.go

@@ -109,7 +109,12 @@ func optimizeStmtList(list []js.IStmt, blockType blockType) []js.IStmt {
 	j := 0                           // write index
 	for i := 0; i < len(list); i++ { // read index
 		if ifStmt, ok := list[i].(*js.IfStmt); ok && !isEmptyStmt(ifStmt.Else) && isFlowStmt(lastStmt(ifStmt.Body)) {
-			// if body ends in flow statement (return, throw, break, continue), so we can remove the else statement and put its body in the current scope
+			// if(!a)b;else c  =>  if(a)c; else b
+			if unary, ok := ifStmt.Cond.(*js.UnaryExpr); ok && unary.Op == js.NotToken {
+				ifStmt.Cond = unary.X
+				ifStmt.Body, ifStmt.Else = ifStmt.Else, ifStmt.Body
+			}
+			// if body ends in flow statement (return, throw, break, continue), we can remove the else statement and put its body in the current scope
 			if blockStmt, ok := ifStmt.Else.(*js.BlockStmt); ok {
 				blockStmt.Scope.Unscope()
 				list = append(list[:i+1], append(blockStmt.List, list[i+1:]...)...)

js/util.go

@@ -366,7 +366,15 @@ func isFlowStmt(stmt js.IStmt) bool {
 
 func lastStmt(stmt js.IStmt) js.IStmt {
 	if block, ok := stmt.(*js.BlockStmt); ok && 0 < len(block.List) {
-		return block.List[len(block.List)-1]
+		return lastStmt(block.List[len(block.List)-1])
+	} else if ifStmt, ok := stmt.(*js.IfStmt); ok {
+		if isEmptyStmt(ifStmt.Else) {
+			if block, ok := ifStmt.Else.(*js.BlockStmt); !ok || len(block.List) == 1 {
+				return lastStmt(ifStmt.Else)
+			}
+		} else if block, ok := ifStmt.Body.(*js.BlockStmt); !ok || len(block.List) == 1 {
+			return lastStmt(ifStmt.Body)
+		}
 	}
 	return stmt
 }