Add basic support for javascript

At the moment, it recognizes simple functions, their params and their
direct return statements.

lua/neogen.lua

@@ -67,10 +67,13 @@ neogen.setup = function(opts)
         languages = {
             lua = require("neogen.configurations.lua"),
             python = require("neogen.configurations.python"),
+            javascript = require("neogen.configurations.javascript")
         },
     })
 
-    neogen.generate_command()
+    if neogen.configuration.enabled == true then
+        neogen.generate_command()
+    end
 end
 
 return neogen

lua/neogen/configurations/javascript.lua

@@ -0,0 +1,40 @@
+return {
+    parent = { "function_declaration" },
+
+    data = {
+        ["function_declaration"] = {
+            ["0"] = {
+
+                extract = function (node)
+                    local results = {}
+                    local tree = {
+                        { retrieve = "first", node_type = "formal_parameters", subtree = {
+                            { retrieve = "all", node_type = "identifier", extract = true }
+                        } },
+                        { retrieve = "first", node_type = "statement_block", subtree = {
+                            { retrieve = "first", node_type = "return_statement", extract = true }
+                        } }
+                    }
+                    local nodes = neogen.utilities.nodes:matching_nodes_from(node, tree)
+                    local res = neogen.utilities.extractors:extract_from_matched(nodes)
+
+                    results.parameters = res.identifier
+                    results.return_statement = res.return_statement
+                    return results
+                end
+            }
+        }
+    },
+
+    template = {
+        annotation_convention = "jsdoc",
+        use_default_comment = false,
+
+        jsdoc = {
+            { nil, "/**" },
+            { "parameters", " * @param {any} %s " },
+            { "return_statement", " * @returns {any} " },
+            { nil, " */" }
+        }
+    }
+}