diff --git a/.gitignore b/.gitignore
index f48aeac5..4334b3d8 100644
--- a/.gitignore
+++ b/.gitignore
@@ -11,6 +11,7 @@
 /qtcreator.creator.user
 /Makefile.conf
 /abc
+/viz.js
 /yosys
 /yosys.exe
 /yosys.js
diff --git a/Makefile b/Makefile
index c762bd38..a7035008 100644
--- a/Makefile
+++ b/Makefile
@@ -113,7 +113,11 @@ LDLIBS =
 EXE = .js
 
 TARGETS := $(filter-out yosys-config,$(TARGETS))
-EXTRA_TARGETS += yosys.html
+EXTRA_TARGETS += yosys.html viz.js
+
+viz.js:
+	wget -O viz.js.part https://github.com/mdaines/viz.js/releases/download/0.0.3/viz.js
+	mv viz.js.part viz.js
 
 yosys.html: misc/yosys.html
 	$(P) cp misc/yosys.html yosys.html
diff --git a/misc/yosys.html b/misc/yosys.html
index 741b88b4..a5a8b65c 100644
--- a/misc/yosys.html
+++ b/misc/yosys.html
@@ -2,7 +2,9 @@
 	<title>yosys.js example application</title>
 </head><body onload="document.getElementById('command').focus()">
 	<h1>yosys.js example application</h1>
-	<div id="tabs"></div>
+	<table width="100%"><tr><td><div id="tabs"></div></td><td align="right"><tt>[ <span onclick="load_example()">load example</span> ]</tt></td></tr></table>
+	<iframe id="viz" style="display: none"><script type="text/javascript" src="viz.js"></script></iframe>
+	<svg id="svg" style="display: none; position: absolute; padding: 10px; width: 100%; height: 80%;"></svg>
 	<div><textarea id="output" style="width: 100%" rows="30" cols="100"></textarea></div>
 	<div id="wait" style="display: block"><br/><b><span id="waitmsg">Loading...</span></b></div>
 	<div id="input" style="display: none"><form onsubmit="window.setTimeout(run_command); return false"><tt><span id="prompt">
@@ -42,6 +44,7 @@
 
 		var current_file = "";
 		var console_messages = "";
+		var svg_cache = { };
 
 		function update_tabs() {
 			var f, html = "", flist = FS.readdir('.');
@@ -62,8 +65,10 @@
 			}
 			html += ' | <span onclick="open_file(prompt(\'Filename:\'))">new file</span> ]</tt>';
 			document.getElementById('tabs').innerHTML = html;
-			if (current_file == "") {
-				document.getElementById('output').readOnly = true;
+			if (current_file == "" || /\.dot$/.test(current_file)) {
+				var element = document.getElementById('output');
+				element.readOnly = true;
+				element.scrollTop = element.scrollHeight; // focus on bottom
 				document.getElementById('command').focus();
 			} else {
 				document.getElementById('output').readOnly = false;
@@ -75,7 +80,7 @@
 		{
 			if (current_file == "")
 				console_messages = document.getElementById('output').value;
-			else
+			else if (!/\.dot$/.test(current_file))
 				FS.writeFile(current_file, document.getElementById('output').value, {encoding: 'utf8'});
 
 			if (filename == "") {
@@ -89,21 +94,74 @@
 				}
 			}
 
+			if (/\.dot$/.test(filename)) {
+				dot = document.getElementById('output').value;
+				if (!(dot in svg_cache)) {
+					el = document.getElementById('viz');
+					svg_cache[dot] = el.contentWindow.Viz(dot, "svg");
+				}
+				document.getElementById('svg').innerHTML = svg_cache[dot];
+				document.getElementById('svg').style.display = 'block';
+				document.getElementById('output').value = '';
+			} else {
+				document.getElementById('svg').innerHTML = '';
+				document.getElementById('svg').style.display = 'none';
+			}
+
 			current_file = filename;
 			update_tabs()
 		}
 
 		function startup() {
+			el = document.getElementById('viz');
+			el.contentWindow.document.open();
+			el.contentWindow.document.write('<script type="text/javascript" src="viz.js"></' + 'script>');
+			el.contentWindow.document.close();
+
 			document.getElementById('wait').style.display = 'none';
 			document.getElementById('input').style.display = 'block';
 			document.getElementById('waitmsg').innerText = 'Waiting for yosys.js...';
 			document.getElementById('prompt').innerText = yosys_prompt();
-			FS.mkdir('/work')
-			FS.chdir('/work')
+
+			try { FS.mkdir('/work'); } catch (e) { }
+			FS.chdir('/work');
+
 			update_tabs();
 			console.log('yosys.js loaded.');
 		}
 
+		function load_example() {
+			open_file('')
+
+			var txt = "";
+			txt += "// a simple yosys.js example. run \"script example.ys\".\n";
+			txt += "\n";
+			txt += "module example(input clk, input rst, input inc, output reg [3:0] cnt);\n";
+			txt += "  always @(posedge clk) begin\n";
+			txt += "    if (rst)\n";
+			txt += "      cnt <= 0;\n";
+			txt += "    else if (inc)\n";
+			txt += "      cnt <= cnt + 1;\n";
+			txt += "  end\n";
+			txt += "endmodule\n";
+			txt += "\n";
+			FS.writeFile('example.v', txt, {encoding: 'utf8'});
+
+			var txt = "";
+			txt += "# a simple yosys.js example. run \"script example.ys\".\n";
+			txt += "\n";
+			txt += "design -reset\n";
+			txt += "read_verilog example.v\n";
+			txt += "proc\n";
+			txt += "opt\n";
+			txt += "show\n";
+			txt += "\n";
+			FS.writeFile('example.ys', txt, {encoding: 'utf8'});
+
+			open_file('example.ys')
+			document.getElementById('command').focus();
+		}
+
 		function yosys_command(cmd) {
 			Module.ccall('run', '', ['string'], [cmd])
 		}
@@ -116,6 +174,9 @@
 			var cmd = document.getElementById('command').value;
 			document.getElementById('command').value = '';
 
+			var show_dot_before = "";
+			try { show_dot_before = FS.readFile('show.dot', { encoding: 'utf8' }); } catch (e) { }
+
 			open_file('');
 			Module.print(yosys_prompt() + cmd);
 
@@ -129,9 +190,17 @@
 					Module.print('Caught JavaScript exception. (see JavaScript console for details.)');
 					console.log(e);
 				}
+
 				document.getElementById('wait').style.display = 'none';
 				document.getElementById('input').style.display = 'block';
 				document.getElementById('prompt').innerText = yosys_prompt();
+
+				var show_dot_after = "";
+				try { show_dot_after = FS.readFile('show.dot', { encoding: 'utf8' }); } catch (e) { }
+
+				if (show_dot_before != show_dot_after)
+					open_file('show.dot');
+
 				update_tabs();
 			}
 
diff --git a/passes/cmds/show.cc b/passes/cmds/show.cc
index 63da29b9..4d6095e5 100644
--- a/passes/cmds/show.cc
+++ b/passes/cmds/show.cc
@@ -650,9 +650,14 @@ struct ShowPass : public Pass {
 		std::vector<std::pair<std::string, RTLIL::Selection>> color_selections;
 		std::vector<std::pair<std::string, RTLIL::Selection>> label_selections;
 
+#ifdef EMSCRIPTEN
+		std::string format = "dot";
+		std::string prefix = "show";
+#else
 		std::string format;
-		std::string viewer_exe;
 		std::string prefix = stringf("%s/.yosys_show", getenv("HOME") ? getenv("HOME") : ".");
+#endif
+		std::string viewer_exe;
 		std::vector<std::string> libfiles;
 		std::vector<RTLIL::Design*> libs;
 		uint32_t colorSeed = 0;
