Enable --screw-ie8 by default.

catch identifier is mangled correctly for ES5 standards-compliant JS engines by default.

Unconditionally use the ie8 if/do-while workaround whether or not --screw-ie8 is enabled.

To support non-standard ie8 javascript use: uglifyjs --support-ie8

lib/compress.js

@@ -72,7 +72,7 @@ function Compressor(options, false_by_default) {
         pure_getters  : false,
         pure_funcs    : null,
         negate_iife   : !false_by_default,
-        screw_ie8     : false,
+        screw_ie8     : true,
         drop_console  : false,
         angular       : false,
         warnings      : true,

lib/output.js

@@ -64,7 +64,7 @@ function OutputStream(options) {
         comments         : false,
         shebang          : true,
         preserve_line    : false,
-        screw_ie8        : false,
+        screw_ie8        : true,
         preamble         : null,
         quote_style      : 0,
         keep_quoted_props: false
@@ -861,8 +861,8 @@ function OutputStream(options) {
         // adds the block brackets if needed.
         if (!self.body)
             return output.force_semicolon();
-        if (self.body instanceof AST_Do
-            && !output.option("screw_ie8")) {
+        if (self.body instanceof AST_Do) {
+            // Unconditionally use the if/do-while workaround for all browsers.
             // https://github.com/mishoo/UglifyJS/issues/#issue/57 IE
             // croaks with "syntax error" on code like this: if (foo)
             // do ... while(cond); else ...  we need block brackets

lib/scope.js

@@ -88,7 +88,7 @@ SymbolDef.prototype = {
 
 AST_Toplevel.DEFMETHOD("figure_out_scope", function(options){
     options = defaults(options, {
-        screw_ie8: false,
+        screw_ie8: true,
         cache: null
     });
 
@@ -377,7 +377,7 @@ AST_Toplevel.DEFMETHOD("_default_mangler_options", function(options){
         eval        : false,
         sort        : false, // Ignored. Flag retained for backwards compatibility.
         toplevel    : false,
-        screw_ie8   : false,
+        screw_ie8   : true,
         keep_fnames : false
     });
 });