Add support for esm and cjs modules

js/embed/pre.js

@@ -0,0 +1,49 @@
+var Module = {
+    stdinData: "",
+    stdoutCallback: null,
+    stderrCallback: null,
+
+    // Function to set a callback for stdout
+    setStdoutCallback: function(callback) {
+        this.stdoutCallback = callback;
+    },
+
+    // Function to set a callback for stderr
+    setStderrCallback: function(callback) {
+        this.stderrCallback = callback;
+    },
+
+    // Function to set input data for stdin
+    setStdinData: function(data) {
+        this.stdinData = data;
+    },
+
+    // `preRun` is called before the program starts running
+    preRun: function() {
+        // Define a custom stdin function
+        function customStdin() {
+            if (Module.stdinData.length === 0) {
+                return null; // End of input (EOF)
+            }
+            const char = Module.stdinData.charCodeAt(0);
+            Module.stdinData = Module.stdinData.slice(1); // Remove the character from input
+            return char;
+        }
+
+        // Define a custom stdout function
+        function customStdout(char) {
+            if (Module.stdoutCallback) {
+                Module.stdoutCallback(String.fromCharCode(char));
+            }
+        }
+
+        // Define a custom stderr function
+        function customStderr(char) {
+            if (Module.stderrCallback) {
+                Module.stderrCallback(String.fromCharCode(char));
+            }
+        }
+
+        FS.init(customStdin, customStdout, customStderr);
+    },
+};