Add leaflet_method decorator

This allows javascript method calls to be generated using
an empty method body and a signature. Useful for writing plugins.

As an example (and the driving motivation) I implemented this on
the geoman plugin.

Author: hansthen

folium/elements.py

@@ -1,3 +1,4 @@
+from functools import wraps
 from typing import List, Tuple
 
 from branca.element import (
@@ -9,7 +10,15 @@
 )
 
 from folium.template import Template
-from folium.utilities import JsCode
+from folium.utilities import JsCode, camelize
+
+
+def leaflet_method(fn):
+    @wraps(fn)
+    def inner(self, *args, **kwargs):
+        self.add_child(MethodCall(self, fn.__name__, *args, **kwargs))
+
+    return inner
 
 
 class JSCSSMixin(MacroElement):
@@ -148,3 +157,27 @@ def __init__(self, element_name: str, element_parent_name: str):
         super().__init__()
         self.element_name = element_name
         self.element_parent_name = element_parent_name
+
+
+class MethodCall(MacroElement):
+    """Abstract class to add an element to another element."""
+
+    _template = Template(
+        """
+        {% macro script(this, kwargs) %}
+            {{ this.target }}.{{ this.method }}(
+                {% for arg in this.args %}
+                    {{ arg | tojavascript }},
+                {% endfor %}
+                {{ this.kwargs | tojavascript }}
+            );
+        {% endmacro %}
+    """
+    )
+
+    def __init__(self, target: MacroElement, method: str, *args, **kwargs):
+        super().__init__()
+        self.target = target.get_name()
+        self.method = camelize(method)
+        self.args = args
+        self.kwargs = kwargs

folium/plugins/geoman.py

@@ -1,6 +1,6 @@
 from branca.element import MacroElement
 
-from folium.elements import JSCSSMixin
+from folium.elements import JSCSSMixin, leaflet_method
 from folium.template import Template
 from folium.utilities import remove_empty
 
@@ -22,6 +22,8 @@ class GeoMan(JSCSSMixin, MacroElement):
     _template = Template(
         """
         {% macro script(this, kwargs) %}
+            /* ensure the name is usable */
+            var {{this.get_name()}} = {{this._parent.get_name()}}.pm;
             {%- if this.feature_group  %}
                 var drawnItems_{{ this.get_name() }} =
                     {{ this.feature_group.get_name() }};
@@ -37,7 +39,7 @@ class GeoMan(JSCSSMixin, MacroElement):
             */
             var drawnItems = drawnItems_{{ this.get_name() }};
 
-            {{this._parent.get_name()}}.pm.addControls(
+            {{this.get_name()}}.addControls(
                 {{this.options|tojavascript}}
             )
             drawnItems_{{ this.get_name() }}.eachLayer(function(layer){
@@ -99,3 +101,7 @@ def __init__(
         self.options = remove_empty(
             position=position, layer_group=feature_group, **kwargs
         )
+
+    @leaflet_method
+    def set_global_options(self, **kwargs):
+        pass