ASP.NET - 在提交表单之前调用javascript验证函数

I need to implement some 3rd-party field validation in our site's forms. Currently, the validation of our form fields is done by using ASP.NET validators (required, regex) and I'd like to continue use of these on the fields where we won't be using the new validation. The company providing us with the new validation services gave us all of the code to integrate into our site to get the new validation functioning, and the basic implementation just requires us to call a javascript method that reads the values of specified fields and validates them via a few service calls. Also, the implementation requires that the form initially has the I need to implement some 3rd-party field valida