feat: Check argv before execution for better UX

src/util.js

@@ -167,7 +167,7 @@ function _global_options(argv) {
   flags.push(def_flag(argv['log-file'], (argv['log-file']) ? '--log-file' : '--no-log-file'));
   flags.push(def_flag(argv['elapsed-time'], (argv['elapsed-time']) ? '--elapsed-time' : '--no-elapsed-time'));
   flags.push(def_flag(argv['no-color'], '--no-color'));
-  /* Number type */
+  /* Numeric type */
   flags.push(def_flag(argv.verbose, '--verbose', argv.verbose));
   /* String type */
   flags.push(def_flag(argv.proxy, '--proxy', argv.proxy));
@@ -177,6 +177,23 @@ function _global_options(argv) {
   return flags;
 }
 
+/**
+ * Check any invalid arguments or options.
+ * @param { JSON } (argv - Argument vector.
+ * @return Return true if there is no input error.
+ */
+function _check_argv(argv) {
+  /* Numeric type */
+  if (argv.verbose !== undefined &&
+      // this must exclude NaN -- yargs default value for numeric type
+      !(argv.verbose >= 0 && argv.verbose <= 5)) {
+    console.warn("invalid value for --verbose option: must be a number between 0 and 5");
+    return false;
+  }
+
+  return true;
+}
+
 /**
  * Form elisp script path.
  * @param { string } name - Name of the script without extension.
@@ -212,6 +229,11 @@ async function e_call(argv, script, ...args) {
     return;
   }
 
+  if (!_check_argv(argv)) {
+    process.exit(1);
+    return;
+  }
+
   return new Promise(resolve => {
     let _path = el_script(script);