[ Language & values ]

@sdxc/iife

Immediately invoke a callback where an expression is needed

Used by: uptime, auth-saas, reader, blog
Source: packages/iife

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Immediately invoke a callback where an expression is needed.

Installation

npm add @sdxc/iife

Usage

Compute a value without an outer mutable binding

import { iife } from "@sdxc/iife";

let buttonLabel = iife(() => {
	if (isSaving) return "Saving…";
	if (hasChanges) return "Save changes";
	return "Saved";
});

Branch in the middle of JSX

import { iife } from "@sdxc/iife";

<header>
	<h1>{team.name}</h1>
	<p>
		{iife(() => {
			if (team.plan === "enterprise") return "Priority support enabled";
			if (team.trialEndsAt) return `Trial ends on ${formatDate(team.trialEndsAt)}`;
			return "Standard support";
		})}
	</p>
</header>;

Keep `try`/`catch` inside the assignment

import { iife } from "@sdxc/iife";

let result = iife(() => {
	try {
		let data = JSON.parse(input) as { name: string };
		return { data: data.name, error: null };
	} catch {
		return { data: null, error: "Invalid JSON input" };
	}
});

Await sequential async work inline

import { iife } from "@sdxc/iife";

let viewer = await iife(async () => {
	let response = await fetch("/api/viewer");
	return response.json() as Promise<{ profileUrl: string }>;
});

let profile = await iife(async () => {
	let response = await fetch(viewer.profileUrl);
	return response.json();
});

API

`iife<T>(fn: () => T): T`

Runs fn immediately and returns its result. An async callback yields a promise; await it like any other.

Pattern: Object fields that need a branch

import { iife } from "@sdxc/iife";

let payload = {
	title: "Invoice",
	status: iife(() => {
		if (isPaid) return "paid";
		if (isOverdue) return "overdue";
		return "pending";
	}),
};