Middlewares.md

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Middlewares

With middlewares, you can extend your command handler even further.

Example

Let's say I want to add a middleware that adds user info to the Custom Context.

One way I could do this is like so:

handler.run(input, {
    ...etcetc,
    userdata: fetchFromDatabase(),
});

But that's very inefficient because it will fetch from the database on every input.

That's where middlewares come in:

handler.use({
    id: "userinfo",
    before: "run",
    run(execCtx, next) {
        execCtx.ctx.userdata = fetchFromDatabase();
        next();
    }
});

The handler will now run this middleware before the run stage.

Stages

The command handler has 5 "stages":

• splitString: User input is splitted for next stage
  • ``
• resolveCommand: The command is resolved from the input
• parseUsages: The usages of the command are parsed, and runArgs are built
• checks: The stage where checks get run.
• run: The final stage. The command gets run here.

You can think of these stages as middlewares too.

Middleware Definition

A middleware is an object with these properties:

• id: string: The identifier for the middleware
• before?: string: If specified, this middleware will be executed before the specified one.
• after?: string: If specified, this middleware will be executed after the specified one.
• requires?: string[]: If specified, the middleware will require all of the supplied ones to execute before itself.
• run: (execCtx, next) => void:
  • The function of the middleware.
  • execCtx is the ExecutorContext
  • next is a function that, when called, will continue running the middlewares.

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