Adding a type guard for AxiosError (#2949)

Co-authored-by: Jason Kwok <JasonHK@users.noreply.github.com>

lib/axios.js

@@ -47,6 +47,9 @@ axios.all = function all(promises) {
 };
 axios.spread = require('./helpers/spread');
 
+// Expose isAxiosError
+axios.isAxiosError = require('./helpers/isAxiosError');
+
 module.exports = axios;
 
 // Allow use of default import syntax in TypeScript

lib/helpers/isAxiosError.js

@@ -0,0 +1,11 @@
+'use strict';
+
+/**
+ * Determines whether the payload is an error thrown by Axios
+ *
+ * @param {*} payload The value to test
+ * @returns {boolean} True if the payload is an error thrown by Axios, otherwise false
+ */
+module.exports = function isAxiosError(payload) {
+  return (typeof payload === 'object') && (payload.isAxiosError === true);
+};