loader.path doesn't need to be in the config. Added prefix.

src/loader/File.js

@@ -83,7 +83,7 @@ var File = new Class({
          * @type {string}
          * @since 3.0.0
          */
-        this.key = GetFastValue(fileConfig, 'key', false);
+        this.key = loader.prefix + GetFastValue(fileConfig, 'key', false);
 
         if (!this.type || !this.key)
         {
@@ -101,11 +101,11 @@ var File = new Class({
 
         if (this.url === undefined)
         {
-            this.url = GetFastValue(fileConfig, 'path', '') + this.key + '.' + GetFastValue(fileConfig, 'extension', '');
+            this.url = loader.path + this.key + '.' + GetFastValue(fileConfig, 'extension', '');
         }
         else if (typeof(this.url) !== 'function')
         {
-            this.url = GetFastValue(fileConfig, 'path', '').concat(this.url);
+            this.url = loader.path + this.url;
         }
 
         /**

src/loader/LoaderPlugin.js

@@ -65,6 +65,9 @@ var LoaderPlugin = new Class({
     {
         EventEmitter.call(this);
 
+        var gameConfig = scene.sys.game.config;
+        var sceneConfig = scene.sys.settings.loader;
+
         /**
          * [description]
          *
@@ -101,22 +104,19 @@ var LoaderPlugin = new Class({
          */
         this.textureManager = scene.sys.textures;
 
-        /**
-         * [description]
-         *
-         * @name Phaser.Loader.LoaderPlugin#_multilist
-         * @type {object}
-         * @private
-         * @default {}
-         * @since 3.0.0
-         */
-        // this._multilist = {};
-
         //  Inject the available filetypes into the Loader
         FileTypesManager.install(this);
 
-        var gameConfig = this.systems.game.config;
-        var sceneConfig = this.systems.settings.loader;
+        /**
+         * An optional prefix that is automatically prepended to the start of every file key.
+         * If prefix was `MENU` and you load an image with the key 'Background' the resulting key would be `MENUBackground`.
+         *
+         * @name Phaser.Loader.LoaderPlugin#prefix
+         * @type {string}
+         * @default ''
+         * @since 3.7.0
+         */
+        this.prefix = '';
 
         /**
          * [description]
@@ -142,6 +142,8 @@ var LoaderPlugin = new Class({
 
         this.setPath(GetFastValue(sceneConfig, 'path', gameConfig.loaderPath));
 
+        this.setPrefix(GetFastValue(sceneConfig, 'prefix', gameConfig.loaderPrefix));
+
         /**
          * [description]
          *
@@ -333,6 +335,26 @@ var LoaderPlugin = new Class({
         return this;
     },
 
+    /**
+     * An optional prefix that is automatically prepended to the start of every file key.
+     * If prefix was `MENU` and you load an image with the key 'Background' the resulting key would be `MENUBackground`.
+     *
+     * @method Phaser.Loader.LoaderPlugin#setPrefix
+     * @since 3.7.0
+     *
+     * @param {string} prefix - The prefix to use. Leave empty to reset.
+     *
+     * @return {Phaser.Loader.LoaderPlugin} This Loader object.
+     */
+    setPrefix: function (prefix)
+    {
+        if (prefix === undefined) { prefix = ''; }
+
+        this.prefix = prefix;
+
+        return this;
+    },
+
     /**
      * [description]
      *

src/loader/filetypes/AudioFile.js

@@ -51,7 +51,6 @@ var AudioFile = new Class({
             responseType: 'arraybuffer',
             key: key,
             url: GetFastValue(url, 'uri', url),
-            path: loader.path,
             xhrSettings: xhrSettings
         };
 

src/loader/filetypes/BinaryFile.js

@@ -53,7 +53,6 @@ var BinaryFile = new Class({
             responseType: 'arraybuffer',
             key: key,
             url: url,
-            path: loader.path,
             xhrSettings: xhrSettings
         };
 

src/loader/filetypes/GLSLFile.js

@@ -53,7 +53,6 @@ var GLSLFile = new Class({
             responseType: 'text',
             key: key,
             url: url,
-            path: loader.path,
             xhrSettings: xhrSettings
         };
 

src/loader/filetypes/HTML5AudioFile.js

@@ -42,7 +42,6 @@ var HTML5AudioFile = new Class({
             extension: GetFastValue(url, 'type', ''),
             key: key,
             url: GetFastValue(url, 'uri', url),
-            path: loader.path,
             config: config
         };
 

src/loader/filetypes/HTMLFile.js

@@ -60,7 +60,6 @@ var HTMLFile = new Class({
             responseType: 'text',
             key: key,
             url: url,
-            path: loader.path,
             xhrSettings: xhrSettings,
             config: {
                 width: width,

src/loader/filetypes/ImageFile.js

@@ -55,7 +55,6 @@ var ImageFile = new Class({
             responseType: 'blob',
             key: key,
             url: url,
-            path: loader.path,
             xhrSettings: xhrSettings,
             config: frameConfig
         };

src/loader/filetypes/JSONFile.js

@@ -55,7 +55,6 @@ var JSONFile = new Class({
             responseType: 'text',
             key: key,
             url: url,
-            path: loader.path,
             xhrSettings: xhrSettings
         };
 

src/loader/filetypes/PluginFile.js

@@ -61,7 +61,6 @@ var PluginFile = new Class({
             responseType: 'text',
             key: key,
             url: url,
-            path: loader.path,
             xhrSettings: xhrSettings
         };
 

src/loader/filetypes/SVGFile.js

@@ -53,7 +53,6 @@ var SVGFile = new Class({
             responseType: 'text',
             key: key,
             url: url,
-            path: loader.path,
             xhrSettings: xhrSettings
         };
 

src/loader/filetypes/ScriptFile.js

@@ -53,7 +53,6 @@ var ScriptFile = new Class({
             responseType: 'text',
             key: key,
             url: url,
-            path: loader.path,
             xhrSettings: xhrSettings
         };
 

src/loader/filetypes/TextFile.js

@@ -53,7 +53,6 @@ var TextFile = new Class({
             responseType: 'text',
             key: key,
             url: url,
-            path: loader.path,
             xhrSettings: xhrSettings
         };
 

src/loader/filetypes/TilemapCSVFile.js

@@ -55,7 +55,6 @@ var TilemapCSVFile = new Class({
             responseType: 'text',
             key: key,
             url: url,
-            path: loader.path,
             xhrSettings: xhrSettings
         };
 

src/loader/filetypes/XMLFile.js

@@ -54,7 +54,6 @@ var XMLFile = new Class({
             responseType: 'text',
             key: key,
             url: url,
-            path: loader.path,
             xhrSettings: xhrSettings
         };