Adding axios.isCancel method

lib/axios.js

@@ -37,6 +37,7 @@ axios.create = function create(defaultConfig) {
 // Expose Cancel & CancelToken
 axios.Cancel = require('./cancel/Cancel');
 axios.CancelToken = require('./cancel/CancelToken');
+axios.isCancel = require('./cancel/isCancel');
 
 // Expose all/spread
 axios.all = function all(promises) {

lib/cancel/Cancel.js

@@ -14,4 +14,6 @@ Cancel.prototype.toString = function toString() {
   return 'Cancel' + (this.message ? ': ' + this.message : '');
 };
 
+Cancel.prototype.__CANCEL__ = true;
+
 module.exports = Cancel;

lib/cancel/isCancel.js

@@ -0,0 +1,5 @@
+'use strict';
+
+module.exports = function isCancel(value) {
+  return !!(value && value.__CANCEL__);
+};