Enable using defs in .byte and .word directives

asm.js

@@ -483,9 +483,7 @@ class Parser {
         const action = { type: Action.DATA, size: 1 };
         const value = this.integer(token);
         if (value == null) {
-            console.error(
+            action.symbol = token;
-                `ERROR: Unexpected token ${token}, expected value`);
-            return;
         } else {
             if (value > 0xff)
                 console.error(`WARNING: Value ${token} is truncated`);
@@ -502,9 +500,7 @@ class Parser {
         const action = { type: Action.DATA, size: 2 };
         const value = this.integer(token);
         if (value == null) {
-            console.error(
+            action.symbol = token;
-                `ERROR: Unexpected token ${token}, expected value`);
-            return;
         } else {
             if (value > 0xffff)
                 console.error(`WARNING: Value ${token} is truncated`);
@@ -723,7 +719,10 @@ export class Assembler {
 
     action_data(action) {
         const data = this.data.at(-1).data;
-        data.push(...action.value);
+        const value = action.value != null
+              ? action.value
+              : this.le_bytes(this.lookup_def(action.symbol), action.size);
+        data.push(...value);
         this.pos.addr += action.size;
     }
 
@@ -762,6 +761,21 @@ export class Assembler {
         return index == -1 ? null : index;
     }
 
+    lookup_def(symbol) {
+        return this.defs[symbol];
+    }
+
+    le_bytes(value, count) {
+        let bytes = []
+        while (value != 0 && bytes.length < count) {
+            bytes.push(value & 0xff);
+            value >>= 8;
+        }
+        while (bytes.length < count)
+            bytes.push(0);
+        return bytes;
+    }
+
     wasm_section_type() {
         const funcs = Object.values(this.funcs);
         const contents = funcs.map(({ params, results }) => {