Use a JS dictionary to initialize a the fields in a Mojo struct

mojo/public/tools/bindings/generators/js_templates/struct_definition.tmpl

 {#--- Begin #}
-  function {{struct.name}}() {
+  function {{struct.name}}(values) {
     this.initDefaults_();
+    this.initFields_(values);
   }
 
 {#--- Enums #}
 {%- from "enum_definition.tmpl" import enum_def %}
 {%  for enum in struct.enums %}
   {{enum_def("%s.%s"|format(struct.name, enum.name), enum, module)}}
-{%  endfor %}
+{%-  endfor %}
 
 {#--- Constants #}
 {%  for constant in struct.constants %}
   {{struct.name}}.{{constant.name}} = {{constant.value|expression_to_text}};
-{%  endfor %}
+{%-  endfor %}
 
-{#--- Set up defaults #}
+{#--- initDefaults() #}
   {{struct.name}}.prototype.initDefaults_ = function() {
 {%- for packed_field in struct.packed.packed_fields %}
     this.{{packed_field.field.name}} = {{packed_field.field|default_value}};
 {%- endfor %}
   };
 
+{#--- initFields() #}
+  {{struct.name}}.prototype.initFields_ = function(fields) {
+    for(var field in fields) {
+        if (this.hasOwnProperty(field))
+          this[field] = fields[field];
+    }
+  };
+
 {#--- Validation #}
 
   {{struct.name}}.validate = function(messageValidator, offset) {
     var err;
 {% macro check_err() -%}
     if (err !== validator.validationError.NONE)
         return err;
 {%- endmacro %}
     err = messageValidator.validateStructHeader(offset, {{struct.name}}.encodedSize, {{struct.packed.packed_fields|length}});
     {{check_err()}}
@@ skipping 64 matching lines @@
 {%-   else %}
 {%-     for packed_field in byte.packed_fields %}
     encoder.{{packed_field.field.kind|encode_snippet}}val.{{packed_field.field.name}});
 {%-     endfor %}
 {%-   endif %}
 {%-   if byte.is_padding %}
     encoder.skip(1);
 {%-   endif %}
 {%- endfor %}
   };