Stopping same param from getting added more than once

runtime/params.spec.ts

@@ -40,6 +40,14 @@ describe('SkyAppRuntimeConfigParams', () => {
     expect(params.getUrl('https://mysite.com?c=d')).toEqual('https://mysite.com?c=d&a1=b');
   });
 
+  it('should not add a current param if the url already has it', () => {
+    const params: SkyAppRuntimeConfigParams = new SkyAppRuntimeConfigParams(
+      '?a1=b',
+      allowed
+    );
+    expect(params.getUrl('https://mysite.com?a1=c&a3=e')).toEqual('https://mysite.com?a1=c&a3=e');
+  });
+
   it('should add the current params to a url without a querystring', () => {
     const params: SkyAppRuntimeConfigParams = new SkyAppRuntimeConfigParams(
       '?a1=b',

runtime/params.ts

@@ -1,5 +1,19 @@
 import { URLSearchParams } from '@angular/http';
 
+/**
+ * Given a "url" (could be just querystring, or fully qualified),
+ * Returns the extracted URLSearchParams.
+ * @param {string} url
+ * @return {URLSearchParams} urlSearchParams
+ */
+function getUrlSearchParams(url: string): URLSearchParams {
+  if (url.indexOf('?') > -1) {
+    url = url.split('?')[1];
+  }
+
+  return new URLSearchParams(url);
+}
+
 export class SkyAppRuntimeConfigParams {
 
   private params: {[key: string]: string} = {};
@@ -9,13 +23,7 @@ export class SkyAppRuntimeConfigParams {
     private allowed: string[]
   ) {
 
-    // Find just the querystring portion of the url
-    if (this.url.indexOf('?') > -1) {
-      this.url = this.url.split('?')[1];
-    }
-
-    // Let angular convert string into object
-    const urlSearchParams: URLSearchParams = new URLSearchParams(this.url);
+    const urlSearchParams: URLSearchParams = getUrlSearchParams(url);
 
     // Filter to allowed params
     this.allowed.forEach(key => {
@@ -63,11 +71,14 @@ export class SkyAppRuntimeConfigParams {
    * @returns {string} url
    */
   public getUrl(url: string): string {
+    const urlSearchParams: URLSearchParams = getUrlSearchParams(url);
     const delimiter = url.indexOf('?') === -1 ? '?' : '&';
     let joined: string[] = [];
 
     this.getAllKeys().forEach(key => {
-      joined.push(`${key}=${encodeURIComponent(this.get(key))}`);
+      if (!urlSearchParams.has(key)) {
+        joined.push(`${key}=${encodeURIComponent(this.get(key))}`);
+      }
     });
 
     return joined.length === 0 ? url : `${url}${delimiter}${joined.join('&')}`;