Crude first pass at playground page

playground/public/shim.js

@@ -0,0 +1,89 @@
+class Buffer extends ArrayBuffer {
+  static alloc(n) {
+
+    return new Buffer(n);
+  }
+  indexOf(n) {
+    let view = new Uint8Array(this);
+    return view.indexOf(n);
+  }
+
+  static concat(bufs) {
+    let size = bufs.reduce((a, b) => (a += b.byteLength), 0);
+    console.log('concat', size, bufs);
+    let rval = new Buffer(size);
+    let view = new Uint8Array(rval);
+    let off = 0;
+    for (let buf of bufs) {
+      view.set(new Uint8Array(buf), off);
+      off += buf.byteLength;
+    }
+    return rval;
+  }
+  toString() {
+    return dec.decode(this)
+  }
+}
+let dec = new TextDecoder();
+let enc = new TextEncoder();
+let files = {
+};
+
+let fds = [];
+
+let shim = {
+  os: {
+    platform() {
+      return "linux";
+    },
+  },
+  fs: {
+    openSync(fn) {
+      console.log("openSync", fn);
+      let te = new TextEncoder();
+      let fd = fds.length;
+      if (!files[fn]) throw new Error(`${fn} not found`)
+      let buf = te.encode(files[fn]);
+      let pos = 0;
+      fds.push({ buf, pos });
+      // we'll mutate the pointer as stuff is read
+      return fd;
+    },
+    readSync(fd, buf, start, len) {
+      let hand = fds[fd]
+      let avail = hand.buf.byteLength - hand.pos
+      let rd = Math.min(avail, len)
+      let src = new Uint8Array(hand.buf)
+      let dest = new Uint8Array(buf)
+      for (let i=0;i<rd;i++)
+        dest[start+i] = src[hand.pos++]
+      console.log('read', rd)
+      return rd
+    },
+    closeSync(fd) {
+      delete fds[fd]
+    }
+  },
+};
+
+shim.fs = new Proxy(shim.fs, {
+  get(target, prop, receiver) {
+    console.log("fs get", prop);
+    return target[prop];
+  },
+});
+
+const process = {
+  platform: "linux",
+  argv: ["", ""],
+  stdout: {
+    // We'll want to replace this one
+    write: console.log,
+  },
+  exit(v) {
+    console.log("exit", v);
+  },
+  // stdin: { fd: 0 },
+};
+
+const require = (x) => shim[x];