JS: Add query for missing await

javascript/ql/test/query-tests/Expressions/MissingAwait/MissingAwait.expected

@@ -0,0 +1,2 @@
+| tst.js:8:9:8:13 | thing | Missing await. The value 'thing' is always a promise. |
+| tst.js:32:12:32:16 | thing | Missing await. The value 'thing' is always a promise. |

javascript/ql/test/query-tests/Expressions/MissingAwait/MissingAwait.qlref

@@ -0,0 +1 @@
+Expressions/MissingAwait.ql

javascript/ql/test/query-tests/Expressions/MissingAwait/tst.js

@@ -0,0 +1,47 @@
+async function getThing() {
+    return something();
+}
+
+function useThing() {
+    let thing = getThing();
+
+    if (thing === undefined) {} // NOT OK
+
+    if (thing == null) {} // NOT OK
+
+    return thing + "bar"; // NOT OK
+}
+
+async function useThingCorrectly() {
+    let thing = await getThing();
+
+    if (thing === undefined) {} // OK
+
+    if (thing == null) {} // OK
+
+    return thing + "bar"; // OK
+}
+
+async function useThingCorrectly2() {
+    let thing = getThing();
+
+    if (await thing === undefined) {} // OK
+
+    if (await thing == null) {} // OK
+
+    return thing + "bar"; // NOT OK
+}
+
+function getThingSync() {
+    return something();
+}
+
+function useThingPossiblySync(b) {
+    let thing = b ? getThing() : getThingSync();
+
+    if (thing === undefined) {} // OK
+
+    if (thing == null) {} // OK
+
+    return thing + "bar"; // NOT OK - but we don't flag it
+}