diff --git a/emscripten/.gitignore b/emscripten/.gitignore
new file mode 100644
index 0000000000000..d5700888a3a2e
--- /dev/null
+++ b/emscripten/.gitignore
@@ -0,0 +1,2 @@
+node_modules/
+
diff --git a/emscripten/Makefile b/emscripten/Makefile
new file mode 100644
index 0000000000000..86b79afc3f27e
--- /dev/null
+++ b/emscripten/Makefile
@@ -0,0 +1,65 @@
+include ../py/mkenv.mk
+
+# clang has slightly different options to GCC
+CLANG = 1
+EMSCRIPTEN = 1
+
+# qstr definitions (must come before including py.mk)
+QSTR_DEFS = qstrdefsport.h
+
+# include py core make definitions
+include ../py/py.mk
+
+CC = emcc -s RESERVED_FUNCTION_POINTERS=20
+CPP = gcc -E
+CLANG = 1
+SIZE = echo
+LD = emcc -s RESERVED_FUNCTION_POINTERS=20
+
+INC += -I.
+INC += -I..
+INC += -I$(BUILD)
+
+CFLAGS = $(INC) -Wall -Werror -ansi -std=gnu99 $(COPT)
+
+#Debugging/Optimization
+ifeq ($(DEBUG), 1)
+CFLAGS += -O0
+CC += -g4
+LD += -g4
+else
+CFLAGS += -Os -DNDEBUG
+endif
+
+CFLAGS += -D MICROPY_NLR_SETJMP=1
+CFLAGS += -D MICROPY_USE_INTERNAL_PRINTF=0
+
+LD = $(CC)
+LDFLAGS = -Wl,-map,$@.map -Wl,-dead_strip -Wl,-no_pie -s EXPORTED_FUNCTIONS="['_mp_js_init', '_mp_js_run']"
+
+LIBS =
+
+SRC_C = \
+	main.c \
+	stdio_core.c \
+	lib/utils/stdout_helpers.c \
+	lib/utils/pyexec.c \
+	lib/mp-readline/readline.c \
+	$(BUILD)/_frozen_mpy.c \
+
+OBJ = $(PY_O) $(addprefix $(BUILD)/, $(SRC_C:.c=.o))
+
+all: $(BUILD)/micropython.js
+
+$(BUILD)/_frozen_mpy.c: frozentest.mpy $(BUILD)/genhdr/qstrdefs.generated.h
+	$(ECHO) "MISC freezing bytecode"
+	$(Q)../tools/mpy-tool.py -f -q $(BUILD)/genhdr/qstrdefs.preprocessed.h -mlongint-impl=none $< > $@
+
+$(BUILD)/micropython.js: $(OBJ)
+	$(ECHO) "LINK $@"
+	$(Q)$(LD) $(LDFLAGS) -o $@ $^ $(LIBS)
+
+run:
+	node repl.js
+
+include ../py/mkrules.mk
diff --git a/emscripten/README.md b/emscripten/README.md
new file mode 100644
index 0000000000000..08a65cb77064e
--- /dev/null
+++ b/emscripten/README.md
@@ -0,0 +1,13 @@
+# MicroPython on Emscripten
+
+Follow the instructions for getting started with Emscripten [here](http://kripken.github.io/emscripten-site/docs/getting_started/downloads.html).
+
+Then you can run
+
+```bash
+source ./emsdk_env.sh
+cd {micropython directory}/emscripten
+make EMSCRIPTEN=1 -j
+node build/firmware.js
+```
+
diff --git a/emscripten/frozentest.mpy b/emscripten/frozentest.mpy
new file mode 100644
index 0000000000000..c8345b1910611
Binary files /dev/null and b/emscripten/frozentest.mpy differ
diff --git a/emscripten/frozentest.py b/emscripten/frozentest.py
new file mode 100644
index 0000000000000..0f99b74297fbb
--- /dev/null
+++ b/emscripten/frozentest.py
@@ -0,0 +1,7 @@
+print('uPy')
+print('a long string that is not interned')
+print('a string that has unicode αβγ chars')
+print(b'bytes 1234\x01')
+print(123456789)
+for i in range(4):
+    print(i)
diff --git a/emscripten/main.c b/emscripten/main.c
new file mode 100644
index 0000000000000..a466a8e8693c1
--- /dev/null
+++ b/emscripten/main.c
@@ -0,0 +1,174 @@
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+
+#include "py/nlr.h"
+#include "py/compile.h"
+#include "py/runtime.h"
+#include "py/repl.h"
+#include "py/gc.h"
+#include "lib/utils/pyexec.h"
+
+#include "emscripten.h"
+
+// TODO: make this work properly with emscripten
+#ifdef _WIN32
+#define PATHLIST_SEP_CHAR ';'
+#else
+#define PATHLIST_SEP_CHAR ':'
+#endif
+
+void do_str(const char *src, mp_parse_input_kind_t input_kind) {
+    mp_lexer_t *lex = mp_lexer_new_from_str_len(MP_QSTR__lt_stdin_gt_, src, strlen(src), 0);
+    if (lex == NULL) {
+        printf("MemoryError: lexer could not allocate memory\n");
+        return;
+    }
+
+    nlr_buf_t nlr;
+    if (nlr_push(&nlr) == 0) {
+        qstr source_name = lex->source_name;
+        mp_parse_tree_t parse_tree = mp_parse(lex, input_kind);
+        mp_obj_t module_fun = mp_compile(&parse_tree, source_name, MP_EMIT_OPT_NONE, true);
+        mp_call_function_0(module_fun);
+        nlr_pop();
+    } else {
+        // uncaught exception
+        mp_obj_print_exception(&mp_plat_print, (mp_obj_t)nlr.ret_val);
+    }
+}
+
+static char *stack_top;
+
+#if MICROPY_ENABLE_GC
+static char heap[2048];
+#endif
+
+struct mp_js_context_t {
+    int(*import_stat) (const char *);
+    const char * (*read_file) (const char *);
+};
+
+static struct mp_js_context_t mp_js_context = {
+    .import_stat = NULL,
+    .read_file = NULL
+};
+
+void mp_js_init(int(*import_stat) (const char *), const char * (*read_file) (const char *)) {
+    gc_init(heap, heap + sizeof(heap));
+    mp_init();
+
+    char *home = getenv("HOME");
+    char *path = getenv("MICROPYPATH");
+    if (path == NULL) {
+        #ifdef MICROPY_PY_SYS_PATH_DEFAULT
+        path = MICROPY_PY_SYS_PATH_DEFAULT;
+        #else
+        path = "~/.micropython/lib:/usr/lib/micropython";
+        #endif
+    }
+    mp_uint_t path_num = 1; // [0] is for current dir (or base dir of the script)
+    for (char *p = path; p != NULL; p = strchr(p, PATHLIST_SEP_CHAR)) {
+        path_num++;
+        if (p != NULL) {
+            p++;
+        }
+    }
+    mp_obj_list_init(MP_OBJ_TO_PTR(mp_sys_path), path_num);
+    mp_obj_t *path_items;
+    mp_obj_list_get(mp_sys_path, &path_num, &path_items);
+    path_items[0] = MP_OBJ_NEW_QSTR(MP_QSTR_);
+
+    {
+        char *p = path;
+        for (mp_uint_t i = 1; i < path_num; i++) {
+            char *p1 = strchr(p, PATHLIST_SEP_CHAR);
+            if (p1 == NULL) {
+                p1 = p + strlen(p);
+            }
+            if (p[0] == '~' && p[1] == '/' && home != NULL) {
+                // Expand standalone ~ to $HOME
+                int home_l = strlen(home);
+                vstr_t vstr;
+                vstr_init(&vstr, home_l + (p1 - p - 1) + 1);
+                vstr_add_strn(&vstr, home, home_l);
+                vstr_add_strn(&vstr, p + 1, p1 - p - 1);
+                path_items[i] = mp_obj_new_str_from_vstr(&mp_type_str, &vstr);
+            } else {
+                path_items[i] = MP_OBJ_NEW_QSTR(qstr_from_strn(p, p1 - p));
+            }
+            p = p1 + 1;
+        }
+    }
+
+    // register file stat and file load functions from JS-side
+    mp_js_context.import_stat = import_stat;
+    mp_js_context.read_file = read_file;
+}
+
+void mp_js_run(const char * code) {
+    do_str(code, MP_PARSE_FILE_INPUT);
+}
+
+void gc_collect(void) {
+    // WARNING: This gc_collect implementation doesn't try to get root
+    // pointers from CPU registers, and thus may function incorrectly.
+    void *dummy;
+    gc_collect_start();
+    gc_collect_root(&dummy, ((mp_uint_t)stack_top - (mp_uint_t)&dummy) / sizeof(mp_uint_t));
+    gc_collect_end();
+    gc_dump_info();
+}
+
+mp_lexer_t *mp_lexer_new_from_file(const char *filename) {
+    if (mp_js_context.read_file == NULL) {
+        return NULL;
+    }
+
+    const char * code_buf = mp_js_context.read_file(filename);
+
+    if (code_buf == NULL) {
+        return NULL;
+    }
+
+    mp_lexer_t* lex = mp_lexer_new_from_str_len(qstr_from_str(filename), code_buf, strlen(code_buf), 0);
+    return lex;
+}
+
+mp_import_stat_t mp_import_stat(const char *path) {
+    if (mp_js_context.import_stat == NULL) {
+        return MP_IMPORT_STAT_NO_EXIST;
+    }
+
+    int s = mp_js_context.import_stat(path);
+
+    if (s == -1) {
+        return MP_IMPORT_STAT_NO_EXIST;
+    } else if (s == 1) {
+        return MP_IMPORT_STAT_DIR;
+    } else {
+        return MP_IMPORT_STAT_FILE;
+    }
+}
+
+mp_obj_t mp_builtin_open(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
+    return mp_const_none;
+}
+MP_DEFINE_CONST_FUN_OBJ_KW(mp_builtin_open_obj, 1, mp_builtin_open);
+
+void nlr_jump_fail(void *val) {
+}
+
+void NORETURN __fatal_error(const char *msg) {
+    while (1);
+}
+
+#ifndef NDEBUG
+void MP_WEAK __assert_func(const char *file, int line, const char *func, const char *expr) {
+    printf("Assertion '%s' failed, at file %s:%d\n", expr, file, line);
+    __fatal_error("Assertion failed");
+}
+#endif
+
diff --git a/emscripten/main.js b/emscripten/main.js
new file mode 100644
index 0000000000000..e91333da1f55b
--- /dev/null
+++ b/emscripten/main.js
@@ -0,0 +1,32 @@
+
+const mpy = require('./build/micropython.js');
+
+module.exports.run = function(code) {
+    mpy.ccall('mp_js_run', 'null', ['string'], [code]);
+}
+
+module.exports.init = function(opts) {
+    var import_wrapped = function(file_ptr) {
+        var filename = mpy.Pointer_stringify(file_ptr);
+
+        if (!opts.import_stat != null) {
+            return opts.import_stat(filename);
+        } else {
+            return 0;
+        }
+    }
+
+    var read_wrapped = function(file_ptr) {
+        var filename = mpy.Pointer_stringify(file_ptr);
+
+        if (opts.read_file != null) {
+            return opts.read_file(filename);
+        } else {
+            return 0;
+        }
+    }
+
+    mpy.ccall('mp_js_init', 'null', ['int', 'int'], [mpy.Runtime.addFunction(import_wrapped), mpy.Runtime.addFunction(read_wrapped)]);
+}
+
+module.exports.Module = mpy;
diff --git a/emscripten/mpconfigport.h b/emscripten/mpconfigport.h
new file mode 100644
index 0000000000000..8812c9b4dd891
--- /dev/null
+++ b/emscripten/mpconfigport.h
@@ -0,0 +1,98 @@
+#include <stdint.h>
+
+// options to control how Micro Python is built
+
+#define MICROPY_QSTR_BYTES_IN_HASH  (1)
+#define MICROPY_QSTR_EXTRA_POOL     mp_qstr_frozen_const_pool
+#define MICROPY_ALLOC_PATH_MAX      (256)
+#define MICROPY_ALLOC_PARSE_CHUNK_INIT (16)
+#define MICROPY_EMIT_X64            (0)
+#define MICROPY_EMIT_THUMB          (0)
+#define MICROPY_EMIT_INLINE_THUMB   (0)
+#define MICROPY_COMP_MODULE_CONST   (0)
+#define MICROPY_COMP_CONST          (0)
+#define MICROPY_COMP_DOUBLE_TUPLE_ASSIGN (0)
+#define MICROPY_COMP_TRIPLE_TUPLE_ASSIGN (0)
+#define MICROPY_MEM_STATS           (0)
+#define MICROPY_DEBUG_PRINTERS      (0)
+#define MICROPY_ENABLE_GC           (1)
+#define MICROPY_GC_ALLOC_THRESHOLD  (0)
+#define MICROPY_REPL_EVENT_DRIVEN   (0)
+#define MICROPY_HELPER_REPL         (1)
+#define MICROPY_HELPER_LEXER_UNIX   (0)
+#define MICROPY_ENABLE_SOURCE_LINE  (0)
+#define MICROPY_ENABLE_DOC_STRING   (0)
+#define MICROPY_ERROR_REPORTING     (MICROPY_ERROR_REPORTING_TERSE)
+#define MICROPY_BUILTIN_METHOD_CHECK_SELF_ARG (0)
+#define MICROPY_PY_ASYNC_AWAIT      (0)
+#define MICROPY_PY_BUILTINS_BYTEARRAY (0)
+#define MICROPY_PY_BUILTINS_MEMORYVIEW (0)
+#define MICROPY_PY_BUILTINS_ENUMERATE (0)
+#define MICROPY_PY_BUILTINS_FILTER  (0)
+#define MICROPY_PY_BUILTINS_FROZENSET (0)
+#define MICROPY_PY_BUILTINS_REVERSED (0)
+#define MICROPY_PY_BUILTINS_SET     (0)
+#define MICROPY_PY_BUILTINS_SLICE   (0)
+#define MICROPY_PY_BUILTINS_PROPERTY (0)
+#define MICROPY_PY_BUILTINS_MIN_MAX (0)
+#define MICROPY_PY___FILE__         (0)
+#define MICROPY_PY_GC               (0)
+#define MICROPY_PY_ARRAY            (0)
+#define MICROPY_PY_ATTRTUPLE        (0)
+#define MICROPY_PY_COLLECTIONS      (0)
+#define MICROPY_PY_MATH             (0)
+#define MICROPY_PY_CMATH            (0)
+#define MICROPY_PY_IO               (0)
+#define MICROPY_PY_STRUCT           (0)
+#define MICROPY_PY_SYS              (0)
+#define MICROPY_MODULE_FROZEN_MPY   (1)
+#define MICROPY_CPYTHON_COMPAT      (0)
+#define MICROPY_LONGINT_IMPL        (MICROPY_LONGINT_IMPL_NONE)
+#define MICROPY_FLOAT_IMPL          (MICROPY_FLOAT_IMPL_NONE)
+
+// type definitions for the specific machine
+
+#define BYTES_PER_WORD (4)
+
+#define MICROPY_MAKE_POINTER_CALLABLE(p) ((void*)((mp_uint_t)(p) | 1))
+
+// This port is intended to be 32-bit, but unfortunately, int32_t for
+// different targets may be defined in different ways - either as int
+// or as long. This requires different printf formatting specifiers
+// to print such value. So, we avoid int32_t and use int directly.
+#define UINT_FMT "%u"
+#define INT_FMT "%d"
+typedef int mp_int_t; // must be pointer size
+typedef unsigned mp_uint_t; // must be pointer size
+
+typedef long mp_off_t;
+
+#define MP_PLAT_PRINT_STRN(str, len) mp_hal_stdout_tx_strn_cooked(str, len) 
+
+// extra built in names to add to the global namespace
+#define MICROPY_PORT_BUILTINS \
+    { MP_OBJ_NEW_QSTR(MP_QSTR_open), (mp_obj_t)&mp_builtin_open_obj },
+
+// We need to provide a declaration/definition of alloca()
+#include <alloca.h>
+
+#define MICROPY_HW_BOARD_NAME "emscripten"
+#define MICROPY_HW_MCU_NAME "asmjs"
+
+#ifdef __linux__
+#define MICROPY_MIN_USE_STDOUT (1)
+#endif
+
+#ifdef __APPLE__
+#define MICROPY_MIN_USE_STDOUT (1)
+#endif
+
+#ifdef __thumb__
+#define MICROPY_MIN_USE_CORTEX_CPU (1)
+#define MICROPY_MIN_USE_STM32_MCU (1)
+#endif
+
+#define MP_STATE_PORT MP_STATE_VM
+
+#define MICROPY_PORT_ROOT_POINTERS \
+    const char *readline_hist[8];
diff --git a/emscripten/mphalport.h b/emscripten/mphalport.h
new file mode 100644
index 0000000000000..60d68bd2d6d50
--- /dev/null
+++ b/emscripten/mphalport.h
@@ -0,0 +1,2 @@
+static inline mp_uint_t mp_hal_ticks_ms(void) { return 0; }
+static inline void mp_hal_set_interrupt_char(char c) {}
diff --git a/emscripten/package.json b/emscripten/package.json
new file mode 100644
index 0000000000000..be2c30881bc35
--- /dev/null
+++ b/emscripten/package.json
@@ -0,0 +1,28 @@
+{
+  "name": "micropython",
+  "version": "1.8.6",
+  "description": "micropython compiled to ASM.js with emscripten",
+  "main": "main.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/micropython/micropython.git"
+  },
+  "keywords": [
+    "python",
+    "emscripten",
+    "repl"
+  ],
+  "bin": "./server.js",
+  "author": "Matthew Else <matthewelse1997@gmail.com>",
+  "license": "MIT",
+  "bugs": {
+    "url": "https://github.com/micropython/micropython/issues"
+  },
+  "homepage": "https://github.com/micropython/micropython#readme",
+  "dependencies": {
+    "minimist": "^1.2.0"
+  }
+}
diff --git a/emscripten/qstrdefsport.h b/emscripten/qstrdefsport.h
new file mode 100644
index 0000000000000..b9cbb1c649450
--- /dev/null
+++ b/emscripten/qstrdefsport.h
@@ -0,0 +1,8 @@
+// qstrs specific to this port
+Q(file)
+Q(mode)
+Q(encoding)
+Q(r)
+Q(buffering)
+Q(heap_lock)
+Q(heap_unlock)
diff --git a/emscripten/server.js b/emscripten/server.js
new file mode 100755
index 0000000000000..5c65fe624831c
--- /dev/null
+++ b/emscripten/server.js
@@ -0,0 +1,50 @@
+#!/usr/bin/env node
+
+var repl = require('repl');
+var mpy = require('./main.js');
+var argv = require('minimist')(process.argv.slice(2));
+var fs = require('fs');
+
+function mpy_eval(cmd, context, filename, callback) {
+      callback(null, mpy.run(cmd)); 
+}
+
+mpy.init({
+    import_stat: function(filename) {
+        try {
+            var stat = fs.statSync(filename);
+
+            if (stat.isDirectory()) {
+                return 1;
+            } else if (stat.isFile()) {
+                return 0;
+            }
+        } catch (e) {
+            return -1;
+        }
+
+        return -1;
+    },
+    read_file: function(filename) {
+        var content = fs.readFileSync(filename, 'utf-8');
+        var ptr = mpy.Module.allocate(mpy.Module.intArrayFromString(content), 'i8', mpy.Module.ALLOC_STACK);
+
+        return ptr;
+    }
+});
+
+if (argv._.length == 1) {
+    var code = fs.readFileSync(argv._[0], "utf-8");
+    mpy.run(code);
+} else if (argv.c) {
+    var code = argv.c;
+    mpy.run(code);
+} else if (argv.m) {
+    var code = 'import ' + argv.m;
+    mpy.run(code);
+} else if (argv._.length == 0) {
+    console.log("MicroPython on asmjs with emscripten");
+    console.log("Type \"help()\" for more information.");
+    repl.start({prompt: '> ', eval: mpy_eval});
+}
+
diff --git a/emscripten/stdio_core.c b/emscripten/stdio_core.c
new file mode 100644
index 0000000000000..1733d1e2631d8
--- /dev/null
+++ b/emscripten/stdio_core.c
@@ -0,0 +1,14 @@
+#include <unistd.h>
+#include "stdio.h"
+#include "py/mpconfig.h"
+
+// Receive single character
+int mp_hal_stdin_rx_chr(void) {
+    unsigned char c = fgetc(stdin);
+    return c;
+}
+
+// Send string of given length
+void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+    fwrite(str, len, 1, stdout); 
+}
diff --git a/py/py.mk b/py/py.mk
index c71ab7a0c8d7b..9ba133521d399 100644
--- a/py/py.mk
+++ b/py/py.mk
@@ -101,11 +101,18 @@ endif
 # py object files
 PY_O_BASENAME = \
 	mpstate.o \
-	nlrx86.o \
+
+# these object files can only be built if we're not using emscripten, since
+# the input files necessary to build them are ASM files.
+ifneq ($(EMSCRIPTEN), 1)
+PY_O_BASENAME += nlrx86.o \
 	nlrx64.o \
 	nlrthumb.o \
 	nlrxtensa.o \
-	nlrsetjmp.o \
+
+endif
+
+PY_O_BASENAME += nlrsetjmp.o \
 	malloc.o \
 	gc.o \
 	qstr.o \