volume and median keys are not always provided by the API

src/types.ts

@@ -54,7 +54,7 @@ export interface Price {
     /**
      * Median Price On The [Steam Community Market](https://steamcommunity.com/market/)
      */
-    median: number;
+    median?: number;
 }
 
 /**
@@ -72,7 +72,7 @@ export interface CleanItem {
     /**
      * Number Of Available Skins On The Steam Market
      */
-    volume: number;
+    volume?: number;
 }
 
 /**
@@ -86,15 +86,15 @@ export interface RawItem {
     /**
      * Median Price On The [Steam Community Market](https://steamcommunity.com/market/)
      */
-    median_price: string;
+    median_price?: string;
     /**
      * Wether the request was successful or not
      */
     success: boolean;
     /**
      * Number Of Available Skins On The Steam Market
      */
-    volume: string;
+    volume?: string;
 }
 
 /**

src/utils.ts

@@ -59,17 +59,23 @@ const determineCurrencySign = (currency: number): string => {
  * @hidden
  */
 export const generateItem = (name: string, response: RawItem, currency: number): Item => {
-    const result = {
+    const result: Item = {
         id: name,
         price: {
             code: determineCurrencyCode(currency),
             lowest: unformat(response.lowest_price),
-            median: unformat(response.median_price),
             sign: determineCurrencySign(currency),
             type: determineCurrencyType(currency),
         },
-        volume: parseInt(response.volume, 10),
     };
 
+    if (response.median_price) {
+        result.price.median = unformat(response.median_price);
+    }
+
+    if (response.volume) {
+        result.volume = parseInt(response.volume, 10);
+    }
+
     return result;
 };