[[FEAT]] Implement support for async iteration

src/jshint.js

@@ -4898,6 +4898,7 @@ var JSHINT = (function() {
   blockstmt("for", function(context) {
     var s, t = state.tokens.next;
     var letscope = false;
+    var isAsync = false;
     var foreachtok = null;
 
     if (t.value === "each") {
@@ -4908,6 +4909,17 @@ var JSHINT = (function() {
       }
     }
 
+    if (state.tokens.next.identifier && state.tokens.next.value === "await") {
+      advance("await");
+      isAsync = true;
+
+      if (!(context & prodParams.async)) {
+        error("E024", state.tokens.curr, "await");
+      } else if (!state.inES9()) {
+        warning("W119", state.tokens.curr, "asynchronous iteration", "9");
+      }
+    }
+
     increaseComplexityCount();
     advance("(");
 
@@ -4996,6 +5008,10 @@ var JSHINT = (function() {
 
     nextop = state.tokens.next;
 
+    if (isAsync && nextop.value !== "of") {
+      error("E066", nextop);
+    }
+
     // if we're in a for (… in|of …) statement
     if (_.includes(["in", "of"], nextop.value)) {
       if (nextop.value === "of") {

src/messages.js

@@ -81,7 +81,8 @@ var errors = {
   E063: "Super property may only be used within method bodies.",
   E064: "Super call may only be used within class method bodies.",
   E065: "Functions defined outside of strict mode with non-simple parameter lists may not " +
-    "enable strict mode."
+    "enable strict mode.",
+  E066: "Asynchronous iteration is only available with for-of loops."
 };
 
 var warnings = {