feat: Allows to register global "Functions" to access from the Mustache instance

mustache.js

@@ -703,6 +703,7 @@ var mustache = {
   Scanner: undefined,
   Context: undefined,
   Writer: undefined,
+  globalFunctions: {},
   /**
    * Allows a user to override the default caching strategy, by providing an
    * object with set, get and clear methods. This can also be used to disable
@@ -749,7 +750,27 @@ mustache.render = function render (template, view, partials, config) {
                         'argument for mustache#render(template, view, partials)');
   }
 
-  return defaultWriter.render(template, view, partials, config);
+  return defaultWriter.render(template, Object.assign({}, mustache.globalFunctions, view), partials, config);
+};
+
+mustache.registerFunction = function registerFunction (name, fn) {
+  if (typeStr(name) !== 'string') {
+    throw new TypeError('String expected on first argument to mustache.registerFunction');
+  }
+
+  if (!isFunction(fn)){
+    throw new TypeError('Function expected on second argument to mustache.registerFunction');
+  }
+
+  if (hasProperty(mustache.globalFunctions, name)){
+    console.warn('Function "' + name + '" is already registered, it will be overridden');
+  }
+
+  mustache.globalFunctions[name] = function globalFunction () {
+    return function run (text, render) {
+      return fn.call(null, render(text));
+    };
+  };
 };
 
 // Export the escaping function so that the user may override it.