added a sample on how to use the parser/walker to instrument some code

Author: mishoo

tmp/instrument.js

@@ -0,0 +1,97 @@
+// sample on how to use the parser and walker API to instrument some code
+
+var jsp = require("uglify-js").parser;
+var pro = require("uglify-js").uglify;
+
+function instrument(code) {
+        var ast = jsp.parse(code, false, true); // true for the third arg specifies that we want
+                                                // to have start/end tokens embedded in the
+                                                // statements
+        var w = pro.ast_walker();
+
+        // we're gonna need this to push elements that we're currently looking at, to avoid
+        // endless recursion.
+        var analyzing = [];
+        function do_stat() {
+                var ret;
+                if (this[0].start && analyzing.indexOf(this) < 0) {
+                        // without the `analyzing' hack, w.walk(this) would re-enter here leading
+                        // to infinite recursion
+                        analyzing.push(this);
+                        ret = [ "splice", // XXX: "block" is safer
+                                [ [ "stat",
+                                    [ "call", [ "name", "trace" ],
+                                      [ [ "string", this[0].toString() ],
+                                        [ "num", this[0].start.line ],
+                                        [ "num", this[0].start.col ],
+                                        [ "num", this[0].end.line ],
+                                        [ "num", this[0].end.col ]]]],
+                                  w.walk(this) ]];
+                        analyzing.pop(this);
+                }
+                return ret;
+        };
+        var new_ast = w.with_walkers({
+                "stat"     : do_stat,
+                "label"    : do_stat,
+                "break"    : do_stat,
+                "continue" : do_stat,
+                "debugger" : do_stat,
+                "var"      : do_stat,
+                "const"    : do_stat,
+                "return"   : do_stat,
+                "throw"    : do_stat,
+                "try"      : do_stat,
+                "defun"    : do_stat,
+                "if"       : do_stat,
+                "while"    : do_stat,
+                "do"       : do_stat,
+                "for"      : do_stat,
+                "for-in"   : do_stat,
+                "switch"   : do_stat,
+                "with"     : do_stat
+        }, function(){
+                return w.walk(ast);
+        });
+        return pro.gen_code(new_ast, { beautify: true });
+}
+
+
+
+
+////// test code follows.
+
+var code = instrument(test.toString());
+console.log(code);
+
+function test() {
+        // simple stats
+        a = 5;
+        c += a + b;
+        "foo";
+
+        // var
+        var foo = 5;
+        const bar = 6, baz = 7;
+
+        // switch block.  note we can't track case lines the same way.
+        switch ("foo") {
+            case "foo":
+                return 1;
+            case "bar":
+                return 2;
+        }
+
+        // for/for in
+        for (var i = 0; i < 5; ++i) {
+                console.log("Hello " + i);
+        }
+        for (var i in [ 1, 2, 3]) {
+                console.log(i);
+        }
+
+        // note however that the following is broken.  I guess we
+        // should add the block brackets in this case...
+        for (var i = 0; i < 5; ++i)
+                console.log("foo");
+}