yii\widgets\MaskedInput::initClientOptions PHP Method

    protected function initClientOptions()
    {
        $options = $this->clientOptions;
        foreach ($options as $key => $value) {
            if (!$value instanceof JsExpression && in_array($key, ['oncomplete', 'onincomplete', 'oncleared', 'onKeyUp', 'onKeyDown', 'onBeforeMask', 'onBeforePaste', 'onUnMask', 'isComplete', 'determineActiveMasksetIndex'], true)) {
                $options[$key] = new JsExpression($value);
            }
        }
        $this->clientOptions = $options;
    }