I've created mixin to dynamically add 'use strict' literal to the start of functions in classes.
First, we need to create cache of keys which contains in second parameter of Ext.define:
  1. (function () {
  2.     var old = Ext4.define,
  3.         del = [
  4.             'extend', 'mixins', 'statics', 'strictMethods',
  5.             'constructor', 'init', 'notStrictMethods', 'initComponent'
  6.         ],
  7.         res;
  8.     // save keys in cache and delete potentially unsafe keys 
  9.     window.StrictCache = {};
  10.     Ext4.define = function (name, data) {
  11.         res = Ext4.Object.getKeys(data);
  12.         if (data.statics) {
  13.             if (Ext4.isArray(data.statics.notStrictMethods)) {
  14.                 del = Ext4.Array.merge(del, data.statics.notStrictMethods);
  15.             }
  16.             res = Ext4.Array.merge(res, Ext4.Object.getKeys(data.statics));
  17.         }
  18.         res = Ext4.Array.unique(res);
  19.         if (Ext4.isArray(data.notStrictMethods)) {
  20.             del = Ext4.Array.merge(del, data.notStrictMethods);
  21.         }
  22.         Ext4.each(del, function (toDelete) {
  23.             Ext4.Array.remove(res, toDelete);
  24.         });
  25.         StrictCache[name] = res;
  26.         return old.apply(this, arguments);
  27.     };
  28. })();

Next, we must to write mixin:
  1. /**
  2.  * @class Lib.StrictMixin
  3.  * Mixin class for 'use strict' 
  4.  * @author guyfawkes
  5.  * @docauthor guyfawkes
  6.  */
  7. Ext4.define('Lib.StrictMixin', {
  8.     onClassMixedIn : function (mixedClass) {
  9.         var fn;
  10.         // mixedClass can be both class prototype or constructor (in this case we need to get function from its prototype)
  11.         // please note we don't break loop when strictMethods were found: it must be both in 'statics' and non-static of ExtJS 4's class
  12.         Ext4.each([mixedClass, mixedClass.prototype], function (obj, index) {
  13.             fn = function(method) {
  14.                 if (Ext4.isFunction(obj[method])) {
  15.                     console && console.info(
  16.                         Ext4.String.format(
  17.                             '{0} found in {1} of {2}',
  18.                             method, (index ? 'constructor prototype' : 'prototype'), obj.$className
  19.                         )
  20.                     );
  21.                     obj[method] = new Function("'use strict';nreturn " + obj[method].toString())();
  22.                 }
  23.             };
  24.             // if we need to loop over all methods, get keys from cache (or we'll get functions from parent classes and got an error
  25.             if (Ext4.isString(obj.strictMethods) && (obj.strictMethods === 'ALL') && Ext4.isString(obj.$className)) {
  26.                 Ext4.each(StrictCache[obj.$className], fn);
  27.             }
  28.             else {
  29.                 // if strictMethods is an array, loop over it
  30.                 if (Ext4.isArray(obj.strictMethods)) {
  31.                     Ext4.each(obj.strictMethods, fn);
  32.                 }
  33.             }
  34.         });
  35.     }
  36. });