fix: added default headers

Author: arpitmalik

src/EventSource.js

@@ -31,17 +31,30 @@ class EventSource {
     this.timeout = options.timeout ?? 0;
     this.timeoutBeforeConnection = options.timeoutBeforeConnection ?? 500;
     this.withCredentials = options.withCredentials || false;
-    this.headers = options.headers || {};
     this.body = options.body || undefined;
     this.debug = options.debug || false;
     this.interval = options.pollingInterval ?? 5000;
     this.lineEndingCharacter = options.lineEndingCharacter || null;
 
+    const defaultHeaders = {
+      Accept: 'text/event-stream',
+      'Cache-Control': 'no-cache',
+      'X-Requested-With': 'XMLHttpRequest',
+    };
+
+    this.headers = {
+      ...defaultHeaders,
+     ...options.headers
+    };
+
     this._xhr = null;
     this._pollTimer = null;
     this._lastIndexProcessed = 0;
 
-    if (!url || (typeof url !== 'string' && typeof url.toString !== 'function')) {
+    if (
+      !url ||
+      (typeof url !== 'string' && typeof url.toString !== 'function')
+    ) {
       throw new SyntaxError('[EventSource] Invalid URL argument.');
     }
 
@@ -76,12 +89,8 @@ class EventSource {
         this._xhr.withCredentials = true;
       }
 
-      this._xhr.setRequestHeader('Accept', 'text/event-stream');
-
-      if (this.headers) {
-        for (const [key, value] of Object.entries(this.headers)) {
-          this._xhr.setRequestHeader(key, value);
-        }
+      for (const [key, value] of Object.entries(this.headers)) {
+        if(value) this._xhr.setRequestHeader(key, value);
       }
 
       if (this.lastEventId !== null) {
@@ -97,23 +106,34 @@ class EventSource {
 
         const xhr = this._xhr;
 
-        this._logDebug(`[EventSource][onreadystatechange] ReadyState: ${XMLReadyStateMap[xhr.readyState] || 'Unknown'}(${xhr.readyState}), status: ${xhr.status}`);
+        this._logDebug(
+          `[EventSource][onreadystatechange] ReadyState: ${XMLReadyStateMap[xhr.readyState] || 'Unknown'
+          }(${xhr.readyState}), status: ${xhr.status}`
+        );
 
-        if (![XMLHttpRequest.DONE, XMLHttpRequest.LOADING].includes(xhr.readyState)) {
+        if (
+          ![XMLHttpRequest.DONE, XMLHttpRequest.LOADING].includes(
+            xhr.readyState
+          )
+        ) {
           return;
         }
 
         if (xhr.status >= 200 && xhr.status < 400) {
           if (this.status === this.CONNECTING) {
             this.status = this.OPEN;
             this.dispatch('open', { type: 'open' });
-            this._logDebug('[EventSource][onreadystatechange][OPEN] Connection opened.');
+            this._logDebug(
+              '[EventSource][onreadystatechange][OPEN] Connection opened.'
+            );
           }
 
           this._handleEvent(xhr.responseText || '');
 
           if (xhr.readyState === XMLHttpRequest.DONE) {
-            this._logDebug('[EventSource][onreadystatechange][DONE] Operation done.');
+            this._logDebug(
+              '[EventSource][onreadystatechange][DONE] Operation done.'
+            );
             this._pollAgain(this.interval, false);
           }
         } else if (xhr.status !== 0) {
@@ -126,7 +146,9 @@ class EventSource {
           });
 
           if (xhr.readyState === XMLHttpRequest.DONE) {
-            this._logDebug('[EventSource][onreadystatechange][ERROR] Response status error.');
+            this._logDebug(
+              '[EventSource][onreadystatechange][ERROR] Response status error.'
+            );
             this._pollAgain(this.interval, false);
           }
         }
@@ -180,10 +202,16 @@ class EventSource {
     if (this.lineEndingCharacter === null) {
       const detectedNewlineChar = this._detectNewlineChar(response);
       if (detectedNewlineChar !== null) {
-        this._logDebug(`[EventSource] Automatically detected lineEndingCharacter: ${JSON.stringify(detectedNewlineChar).slice(1, -1)}`);
+        this._logDebug(
+          `[EventSource] Automatically detected lineEndingCharacter: ${JSON.stringify(
+            detectedNewlineChar
+          ).slice(1, -1)}`
+        );
         this.lineEndingCharacter = detectedNewlineChar;
       } else {
-        console.warn("[EventSource] Unable to identify the line ending character. Ensure your server delivers a standard line ending character: \\r\\n, \\n, \\r, or specify your custom character using the 'lineEndingCharacter' option.");
+        console.warn(
+          '[EventSource] Unable to identify the line ending character. Ensure your server delivers a standard line ending character: \\r\\n, \\n, \\r, or specify your custom character using the 'lineEndingCharacter' option.'
+        );
         return;
       }
     }
@@ -193,7 +221,10 @@ class EventSource {
       return;
     }
 
-    const parts = response.substring(this._lastIndexProcessed, indexOfDoubleNewline).split(this.lineEndingCharacter);
+    const parts = response
+      .substring(this._lastIndexProcessed, indexOfDoubleNewline)
+      .split(this.lineEndingCharacter);
+
     this._lastIndexProcessed = indexOfDoubleNewline;
 
     let type = undefined;
@@ -250,7 +281,8 @@ class EventSource {
   }
 
   _getLastDoubleNewlineIndex(response) {
-    const doubleLineEndingCharacter = this.lineEndingCharacter + this.lineEndingCharacter;
+    const doubleLineEndingCharacter =
+      this.lineEndingCharacter + this.lineEndingCharacter;
     const lastIndex = response.lastIndexOf(doubleLineEndingCharacter);
     if (lastIndex === -1) {
       return -1;
@@ -269,7 +301,9 @@ class EventSource {
 
   removeEventListener(type, listener) {
     if (this.eventHandlers[type] !== undefined) {
-      this.eventHandlers[type] = this.eventHandlers[type].filter((handler) => handler !== listener);
+      this.eventHandlers[type] = this.eventHandlers[type].filter(
+        (handler) => handler !== listener
+      );
     }
   }
 
@@ -282,7 +316,9 @@ class EventSource {
       }
     } else {
       if (!availableTypes.includes(type)) {
-        throw Error(`[EventSource] '${type}' type is not supported event type.`);
+        throw Error(
+          `[EventSource] '${type}' type is not supported event type.`
+        );
       }
 
       this.eventHandlers[type] = [];