Js error on android 5.1 and lower

Hello guyz my ionic app is wroking very well in android 6 and above but while testing it in android 5.1 and lower
it gives out error:

TypeError: undefined is not a function
    at Array.findBy (file:///android_asset/www/js/app.js:35:17)
    at Object.$scope.vEvents.initApp (file:///android_asset/www/js/controllers/languagesCtrl.js:20:51)
    at fn (eval at <anonymous> (file:///android_asset/www/lib/ionic/js/ionic.bundle.js:27643:15), <anonymous>:4:249)
    at file:///android_asset/www/lib/ionic/js/ionic.bundle.js:65429:9
    at Scope.$eval (file:///android_asset/www/lib/ionic/js/ionic.bundle.js:30400:28)
    at Scope.$apply (file:///android_asset/www/lib/ionic/js/ionic.bundle.js:30500:25)
    at HTMLAnchorElement.<anonymous> (file:///android_asset/www/lib/ionic/js/ionic.bundle.js:65428:13)
    at defaultHandlerWrapper (file:///android_asset/www/lib/ionic/js/ionic.bundle.js:16792:11)
    at HTMLAnchorElement.eventHandler (file:///android_asset/www/lib/ionic/js/ionic.bundle.js:16780:9)
    at triggerMouseEvent (file:///android_asset/www/lib/ionic/js/ionic.bundle.js:2953:7)

I am defining array findby method which works well in android 6 and above

Array.prototype.findBy = function(key, value) {
		function iter(item) {
			if(item[key] === value) {
				return true;
			return false;

		return this.find(iter);

It looks like ionic is unable to read the find() method

Is find available in Android 5.1 and below?
Often it is not the Android version that is responsible, but the version of the Webview active on the device.