Back in the 90s the company I was at wanted to have a crack at some early ASP programming (predating ASP.Net). But because they were a Microsoft shop they had

Back in the 90s the company I was at wanted to have a crack at some early ASP programming (predating ASP.Net). But because they were a Microsoft shop they had decided that they were going to have all the client side events in VBScript (don't ask why, down that path lies madness). So faced with the choice of an ASP page with a mix of client side VBScript and server side VBScript it was pretty hard, so I switched the server side to Javascript (or ECMAScript or JScript or whatever Micorsoft's implementation was called that week). That made the demarcation between client and server (in the same source file) enormously much more clear. Consequently productivity went way up when we did that. I still think that was the wrong way round (Javascript on the client, VBScript on the server would have been better in every single way), but having the two languages was definitely the way to go. Yes, you need to context switch, but when you switch from client to server you need to context switch anyway.