enable no-var rule and fix violations (#1675)

Author: koddsson

eslint.config.js

@@ -14,6 +14,7 @@ export default [
       }
     },
     rules: {
+      "no-var": "error",
       "jsdoc/require-param-description": "off",
       "jsdoc/require-returns-description": "off",
       "jsdoc/tag-lines": ["error", "any", { startLines: 1 }],

lib/chai/assertion.js

@@ -136,21 +136,21 @@ Assertion.prototype.assert = function (
   _actual,
   showDiff
 ) {
-  var ok = util.test(this, arguments);
+  let ok = util.test(this, arguments);
   if (false !== showDiff) showDiff = true;
   if (undefined === expected && undefined === _actual) showDiff = false;
   if (true !== config.showDiff) showDiff = false;
 
   if (!ok) {
     msg = util.getMessage(this, arguments);
-    var actual = util.getActual(this, arguments);
-    var assertionErrorObjectProperties = {
+    let actual = util.getActual(this, arguments);
+    let assertionErrorObjectProperties = {
       actual: actual,
       expected: expected,
       showDiff: showDiff
     };
 
-    var operator = util.getOperator(this, arguments);
+    let operator = util.getOperator(this, arguments);
     if (operator) {
       assertionErrorObjectProperties.operator = operator;
     }