build: add ESLint to script/lint and containerize linting (closes #152)

tests/e2e/firefox/driver.js

@@ -88,7 +88,7 @@ class Driver {
         let parsed;
         try {
             parsed = JSON.parse(text);
-        } catch (_) {
+        } catch {
             throw new Error(
                 method + " " + path + ": non-JSON response: " + text,
             );
@@ -229,7 +229,9 @@ class Driver {
     // condition it was waiting on rather than "timed out".
     async waitFor(what, script, args = [], timeout = DEFAULT_WAIT_MS) {
         const deadline = Date.now() + timeout;
-        let last = null;
+        // Assigned on every path through the loop body before it is read, so
+        // there is no initializer to give it.
+        let last;
         for (;;) {
             try {
                 const v = await this.execute(script, args);
@@ -512,7 +514,7 @@ async function waitForDriverReady(base, timeoutMs) {
                 const body = await res.json();
                 if (body && body.value && body.value.ready !== false) return;
             }
-        } catch (_) {
+        } catch {
             // not listening yet
         }
         if (Date.now() >= deadline) {