added fetch interceptor to the Backend Options

i18nextHttpBackend.js

@@ -36,8 +36,8 @@ function _classCallCheck(instance, Constructor) { if (!(instance instanceof Cons
 function _defineProperties(target, props) { for (var i = 0; i < props.length; i++) { var descriptor = props[i]; descriptor.enumerable = descriptor.enumerable || false; descriptor.configurable = true; if ("value" in descriptor) descriptor.writable = true; Object.defineProperty(target, _toPropertyKey(descriptor.key), descriptor); } }
 function _createClass(Constructor, protoProps, staticProps) { if (protoProps) _defineProperties(Constructor.prototype, protoProps); if (staticProps) _defineProperties(Constructor, staticProps); Object.defineProperty(Constructor, "prototype", { writable: false }); return Constructor; }
 function _defineProperty(obj, key, value) { key = _toPropertyKey(key); if (key in obj) { Object.defineProperty(obj, key, { value: value, enumerable: true, configurable: true, writable: true }); } else { obj[key] = value; } return obj; }
-function _toPropertyKey(arg) { var key = _toPrimitive(arg, "string"); return _typeof(key) === "symbol" ? key : String(key); }
-function _toPrimitive(input, hint) { if (_typeof(input) !== "object" || input === null) return input; var prim = input[Symbol.toPrimitive]; if (prim !== undefined) { var res = prim.call(input, hint || "default"); if (_typeof(res) !== "object") return res; throw new TypeError("@@toPrimitive must return a primitive value."); } return (hint === "string" ? String : Number)(input); }
+function _toPropertyKey(t) { var i = _toPrimitive(t, "string"); return "symbol" == _typeof(i) ? i : String(i); }
+function _toPrimitive(t, r) { if ("object" != _typeof(t) || !t) return t; var e = t[Symbol.toPrimitive]; if (void 0 !== e) { var i = e.call(t, r || "default"); if ("object" != _typeof(i)) return i; throw new TypeError("@@toPrimitive must return a primitive value."); } return ("string" === r ? String : Number)(t); }
 var getDefaults = function getDefaults() {
   return {
     loadPath: '/locales/{{lng}}/{{ns}}.json',
@@ -227,8 +227,8 @@ function _interopRequireWildcard(e, r) { if (!r && e && e.__esModule) return e;
 function ownKeys(e, r) { var t = Object.keys(e); if (Object.getOwnPropertySymbols) { var o = Object.getOwnPropertySymbols(e); r && (o = o.filter(function (r) { return Object.getOwnPropertyDescriptor(e, r).enumerable; })), t.push.apply(t, o); } return t; }
 function _objectSpread(e) { for (var r = 1; r < arguments.length; r++) { var t = null != arguments[r] ? arguments[r] : {}; r % 2 ? ownKeys(Object(t), !0).forEach(function (r) { _defineProperty(e, r, t[r]); }) : Object.getOwnPropertyDescriptors ? Object.defineProperties(e, Object.getOwnPropertyDescriptors(t)) : ownKeys(Object(t)).forEach(function (r) { Object.defineProperty(e, r, Object.getOwnPropertyDescriptor(t, r)); }); } return e; }
 function _defineProperty(obj, key, value) { key = _toPropertyKey(key); if (key in obj) { Object.defineProperty(obj, key, { value: value, enumerable: true, configurable: true, writable: true }); } else { obj[key] = value; } return obj; }
-function _toPropertyKey(arg) { var key = _toPrimitive(arg, "string"); return _typeof(key) === "symbol" ? key : String(key); }
-function _toPrimitive(input, hint) { if (_typeof(input) !== "object" || input === null) return input; var prim = input[Symbol.toPrimitive]; if (prim !== undefined) { var res = prim.call(input, hint || "default"); if (_typeof(res) !== "object") return res; throw new TypeError("@@toPrimitive must return a primitive value."); } return (hint === "string" ? String : Number)(input); }
+function _toPropertyKey(t) { var i = _toPrimitive(t, "string"); return "symbol" == _typeof(i) ? i : String(i); }
+function _toPrimitive(t, r) { if ("object" != _typeof(t) || !t) return t; var e = t[Symbol.toPrimitive]; if (void 0 !== e) { var i = e.call(t, r || "default"); if ("object" != _typeof(i)) return i; throw new TypeError("@@toPrimitive must return a primitive value."); } return ("string" === r ? String : Number)(t); }
 function _typeof(o) { "@babel/helpers - typeof"; return _typeof = "function" == typeof Symbol && "symbol" == typeof Symbol.iterator ? function (o) { return typeof o; } : function (o) { return o && "function" == typeof Symbol && o.constructor === Symbol && o !== Symbol.prototype ? "symbol" : typeof o; }, _typeof(o); }
 var fetchApi;
 if (typeof fetch === 'function') {
@@ -269,7 +269,7 @@ var addQueryString = function addQueryString(url, params) {
   }
   return url;
 };
-var fetchIt = function fetchIt(url, fetchOptions, callback) {
+var fetchIt = function fetchIt(url, fetchOptions, callback, altFetch) {
   var resolver = function resolver(response) {
     if (!response.ok) return callback(response.statusText || 'Error', {
       status: response.status
@@ -281,6 +281,13 @@ var fetchIt = function fetchIt(url, fetchOptions, callback) {
       });
     }).catch(callback);
   };
+  if (altFetch) {
+    var altResponse = altFetch(url, fetchOptions);
+    if (altResponse instanceof Promise) {
+      altResponse.then(resolver).catch(callback);
+      return;
+    }
+  }
   if (typeof fetch === 'function') {
     fetch(url, fetchOptions).then(resolver).catch(callback);
   } else {
@@ -303,8 +310,9 @@ var requestWithFetch = function requestWithFetch(options, url, payload, callback
     body: payload ? options.stringify(payload) : undefined,
     headers: headers
   }, omitFetchOptions ? {} : reqOptions);
+  var altFetch = typeof options.alternateFetch === 'function' && options.alternateFetch.length >= 1 ? options.alternateFetch : undefined;
   try {
-    fetchIt(url, fetchOptions, callback);
+    fetchIt(url, fetchOptions, callback, altFetch);
   } catch (e) {
     if (!reqOptions || Object.keys(reqOptions).length === 0 || !e.message || e.message.indexOf('not implemented') < 0) {
       return callback(e);
@@ -313,7 +321,7 @@ var requestWithFetch = function requestWithFetch(options, url, payload, callback
       Object.keys(reqOptions).forEach(function (opt) {
         delete fetchOptions[opt];
       });
-      fetchIt(url, fetchOptions, callback);
+      fetchIt(url, fetchOptions, callback, altFetch);
       omitFetchOptions = true;
     } catch (err) {
       callback(err);

index.d.ts

@@ -9,7 +9,21 @@ type AddPathOption =
   | string
   | ((lng: string, namespace: string) => string);
 
+type FetchFunction = (input: string, init: RequestInit) => Promise<Response> | void
+
 export interface HttpBackendOptions {
+  /**
+   * Use an alternative fetch function that acts like an interecept, (usefull for low level mocks/simulations)
+   * 
+   * This option is not called if:
+   * 
+   * 1. There is an custom value set for the "request" property in this options object.
+   * 2. The backend selected xmlHttpRequest over fetch
+   * 
+   * If the function is called and it returns anything BUT a promise the fetch or xmlHttpRequest will be subsequentially called
+   * 
+   */
+  alternateFetch?: FetchFunction;
   /**
    * path where resources get loaded from, or a function
    * returning a path:

lib/request.js

@@ -43,13 +43,22 @@ const addQueryString = (url, params) => {
   return url
 }
 
-const fetchIt = (url, fetchOptions, callback) => {
+const fetchIt = (url, fetchOptions, callback, altFetch) => {
   const resolver = (response) => {
     if (!response.ok) return callback(response.statusText || 'Error', { status: response.status })
     response.text().then((data) => {
       callback(null, { status: response.status, data })
     }).catch(callback)
   }
+  if (altFetch) {
+    // already checked to have the proper signature
+    const altResponse = altFetch(url, fetchOptions)
+    if (altResponse instanceof Promise) {
+      altResponse.then(resolver).catch(callback)
+      return
+    }
+    // fall through
+  }
   if (typeof fetch === 'function') { // react-native debug mode needs the fetch function to be called directly (no alias)
     fetch(url, fetchOptions).then(resolver).catch(callback)
   } else {
@@ -78,8 +87,9 @@ const requestWithFetch = (options, url, payload, callback) => {
     headers,
     ...(omitFetchOptions ? {} : reqOptions)
   }
+  const altFetch = typeof options.alternateFetch === 'function' && options.alternateFetch.length >= 1 ? options.alternateFetch : undefined
   try {
-    fetchIt(url, fetchOptions, callback)
+    fetchIt(url, fetchOptions, callback, altFetch)
   } catch (e) {
     if (!reqOptions || Object.keys(reqOptions).length === 0 || !e.message || e.message.indexOf('not implemented') < 0) {
       return callback(e)
@@ -88,7 +98,7 @@ const requestWithFetch = (options, url, payload, callback) => {
       Object.keys(reqOptions).forEach((opt) => {
         delete fetchOptions[opt]
       })
-      fetchIt(url, fetchOptions, callback)
+      fetchIt(url, fetchOptions, callback, altFetch)
       omitFetchOptions = true
     } catch (err) {
       callback(err)

package.json

@@ -77,7 +77,7 @@
     "compile": "npm run compile:esm && npm run compile:cjs",
     "browser": "browserify --ignore cross-fetch --standalone i18nextHttpBackend cjs/index.js -o i18nextHttpBackend.js && uglifyjs i18nextHttpBackend.js --compress --mangle -o i18nextHttpBackend.min.js",
     "build": "npm run compile && npm run browser",
-    "test:xmlhttpreq": "mocha test -R spec --require test/fixtures/xmlHttpRequest.cjs --exit --experimental-modules",
+    "test:xmlhttpreq": "mocha  test -R spec --require test/fixtures/xmlHttpRequest.cjs --exit --experimental-modules",
     "test:fetch": "mocha test -R spec --exit --experimental-modules",
     "test": "npm run lint && npm run build && npm run test:fetch && npm run test:xmlhttpreq && npm run test:typescript",
     "test:typescript": "tslint --project tsconfig.json && tsd",

test/http.spec.js

@@ -12,25 +12,82 @@ describe(`http backend using ${hasXMLHttpRequest() ? 'XMLHttpRequest' : 'fetch'}
 
   describe('#read', () => {
     let backend
+    const logs = []
 
-    before(() => {
+    before(function () {
+      logs.splice(0)
       backend = new Http(
         {
           interpolator: i18next.services.interpolator
         },
         {
-          loadPath: 'http://localhost:5001/locales/{{lng}}/{{ns}}'
+          loadPath: 'http://localhost:5001/locales/{{lng}}/{{ns}}',
+          alternateFetch: (url, requestInit) => {
+            logs.push([url, requestInit])
+            // not returning a promise olding actual data makes this a spy
+            return undefined
+          }
         }
       )
     })
+    if (!hasXMLHttpRequest()) {
+      it('should load data', async () => {
+        let errO
+        let dataO
+        const done = await new Promise((resolve, reject) => {
+          backend.read('en', 'test', (err, data) => {
+            // dont check here with "except", if there is an error
+            // because the test will just "hang" with no further info
+            errO = err
+            dataO = data
+            resolve(true)
+            setTimeout(() => reject(new Error('timeout')), 1500)
+          })
+        })
+        // evaluate outside callback to get actuall error when something is wrong
+        expect(errO).to.be(null)
+        expect(dataO).to.eql({ key: 'passing' })
+        expect(done).to.be(true)
+        expect(logs).to.eql([
+          [
+            'http://localhost:5001/locales/en/test',
+            {
+              method: 'GET',
+              headers: {
+                'User-Agent': 'i18next-http-backend (node/v20.8.0; linux x64)'
+              },
+              mode: 'cors',
+              credentials: 'same-origin',
+              cache: 'default',
+              body: undefined
+            }
+          ]
+        ])
+      })
+    }
 
-    it('should load data', (done) => {
-      backend.read('en', 'test', (err, data) => {
-        expect(err).not.to.be.ok()
-        expect(data).to.eql({ key: 'passing' })
-        done()
+    if (hasXMLHttpRequest()) {
+      it('should load data', async () => {
+        let errO
+        let dataO
+        const done = await new Promise((resolve, reject) => {
+          backend.read('en', 'test', (err, data) => {
+            // dont check here with "except", if there is an error
+            // because the test will just "hang" with no further info
+            errO = err
+            dataO = data
+            resolve(true)
+            setTimeout(() => reject(new Error('timeout')), 1500)
+          })
+        })
+        // evaluate outside callback to get actuall error when something is wrong
+        expect(errO).to.be(null)
+        expect(dataO).to.eql({ key: 'passing' })
+        expect(done).to.be(true)
+        // fetch was not used
+        expect(logs).to.eql([])
       })
-    })
+    }
 
     it('should throw error on not existing file', (done) => {
       backend.read('en', 'notexisting', (err, data) => {