use bind this in expression evaluation

Author: Steffan

src/fields.vue

@@ -78,14 +78,13 @@
 
                 if (isString(expr)) {
 
-                    const $values = {};
-                    const context = {$match, $values};
+                    const context = {$match, $values: values};
 
                     each(config, ({name = key}, key) =>
-                        set($values, name, get(values, name))
+                        set(context, name, get(values, name))
                     );
 
-                    return evaluate(expr, assign(context, $values));
+                    return evaluate(this, expr, assign(context, values));
                 }
 
                 return expr.call(this, values, this);

src/util.js

@@ -64,10 +64,10 @@ export function set(obj, key, val) {
     _set(obj, parts.shift(), val);
 }
 
-export function evaluate(expr, context) {
+export function evaluate(self, expr, context) {
 
     try {
-        return (Function(`with(this){return ${expr}}`)).call(context);
+        return (Function('c', `with(c){return ${expr}}`)).call(self, context);
     } catch (e) {
         warn(e);
     }