fix(core): fix buildUrlParams array handling and replace deprecated substr

Two fixes in buildUrlParams function:
1. Assign slice result to remove trailing '&' from array parameters
2. Replace deprecated substr() with substring()

Before: buildUrlParams({tags: ['a', 'b']}) returned 'tags=a&tags=b&&...'
After: buildUrlParams({tags: ['a', 'b']}) returns 'tags=a&tags=b&...'

Fixes: Double ampersand in URL parameters with arrays
Fixes: Deprecated substr usage

Author: maniktyagi04

core/src/core-plugins.ts

@@ -318,7 +318,7 @@ const normalizeHttpHeaders = (headers: HttpHeaders = {}): HttpHeaders => {
  * @param params A map of url parameters
  * @param shouldEncode true if you should encodeURIComponent() the values (true by default)
  */
-const buildUrlParams = (params?: HttpParams, shouldEncode = true): string | null => {
+export const buildUrlParams = (params?: HttpParams, shouldEncode = true): string | null => {
   if (!params) return null;
 
   const output = Object.entries(params).reduce((accumulator, entry) => {
@@ -333,7 +333,7 @@ const buildUrlParams = (params?: HttpParams, shouldEncode = true): string | null
         item += `${key}=${encodedValue}&`;
       });
       // last character will always be "&" so slice it off
-      item.slice(0, -1);
+      item = item.slice(0, -1);
     } else {
       encodedValue = shouldEncode ? encodeURIComponent(value) : value;
       item = `${key}=${encodedValue}`;
@@ -343,7 +343,7 @@ const buildUrlParams = (params?: HttpParams, shouldEncode = true): string | null
   }, '');
 
   // Remove initial "&" from the reduce
-  return output.substr(1);
+  return output.substring(1);
 };
 
 /**

core/src/tests/http.spec.ts

@@ -0,0 +1,34 @@
+/**
+ * @jest-environment jsdom
+ */
+
+import { buildUrlParams } from '../core-plugins';
+
+describe('buildUrlParams', () => {
+  it('should handle array parameters correctly', () => {
+    const params = {
+      tags: ['javascript', 'typescript', 'react'],
+      single: 'value',
+    };
+
+    const result = buildUrlParams(params, true);
+    
+    // The bug: array values will have a trailing \u0026
+    // Expected: "tags=javascript\u0026tags=typescript\u0026tags=react\u0026single=value"
+    // Actual: "tags=javascript\u0026tags=typescript\u0026tags=react\u0026\u0026single=value"
+    
+    expect(result).not.toContain('\u0026\u0026');
+    expect(result).toBe('tags=javascript\u0026tags=typescript\u0026tags=react\u0026single=value');
+  });
+
+  it('should remove initial ampersand', () => {
+    const params = {
+      key: 'value',
+    };
+
+    const result = buildUrlParams(params, true);
+    
+    expect(result).toBe('key=value');
+    expect(result?.[0]).not.toBe('\u0026');
+  });
+});