I want to use the jsgrid in a customized sitecore shell model , i wonder what could be the best way to include the script file without building a custom speak component.
There are multiple ways to do this. I know you said a custom SPEAK component, but I thought I provide various ways of adding JS into Sitecore:
Read my blog where I include the name of the placeholder on the "Add here" button in Experience Editor. I don't think this is what you need but should give you some ideas.
If you are using the PageCode rendering, there's a PageCodeScriptFilename that you use to load a JS file. See this Sitecore walkthrough for details.
Use a SPEAK client pipeline. Take a look at this example.