Vue with the Composition API

From mental model to working change

Good work on Vue with the Composition API leaves evidence: a visible behavior, a stable contract or a repeatable operational check. This decision shapes the frontend boundary: what is rendered, what becomes interactive, and which state is allowed to cross into another component or route.

Here, that decision supports a specific checkpoint: Rebuild one CourseFlow feature with a deliberate state boundary, then document when an alternative framework would be justified. A reviewable result should include a focused component test, an accessibility check and a before/after browser trace rather than a claim that the feature simply works.

A practical model for vue with the composition api

Build the same progress interaction with Vue so you can compare component models using evidence, not stereotypes. The useful unit of understanding is the boundary: who owns the decision, which input crosses it, what result is visible and how a failure is reported.

• Single-file Components: Locate this responsibility in CourseFlow and defend the boundary you chose.
• Reactive State: Implement one behavior that another learner can reproduce without reading your mind.
• Computed Values: Compare the simplest correct approach with one credible alternative.
• Component Events: State the assumption this concept relies on and show how the system behaves when it is false.

Engineering decisions for Vue with the Composition API

These are the details that separate a working demonstration from a maintainable production decision.

• Composition functions are most useful when they group behavior, not when they merely relocate every line from a component.
• Treat emitted events as a component contract; name the user outcome rather than the DOM gesture.
• Compare bundle, team skill and ecosystem requirements before choosing Vue over an existing stable stack.

Follow the data through the example

The sample is intentionally narrow. Its job is to expose single-file components without hiding the decision behind unrelated setup.

<script setup lang="ts">
import { computed, ref } from 'vue';

const completed = ref(new Set<string>());
const count = computed(() => completed.value.size);

function complete(id: string) {
  completed.value = new Set(completed.value).add(id);
}
</script>

<template>
  <button @click="complete('html-1')">Complete lesson</button>
  <output>{{ count }} complete</output>
</template>

Ship a reviewable increment

1. 1
   Single-file Components

   Name the caller and the owner of this behavior before changing the implementation.

2. 2
   Reactive State

   Compare expected and actual output before editing; the difference tells you where to investigate.

3. 3
   Computed Values

   Keep names tied to the product rule so a reviewer can follow the change without decoding abbreviations.

4. 4
   Component Events

   Add a regression check close to the boundary where this behavior can fail.

Check your reasoning

What to carry into the next lesson

• Build the same progress interaction with Vue so you can compare component models using evidence, not stereotypes.
• Keep single-file components visible at the boundary where it can be tested.
• Use evidence from reactive state before widening the implementation.

References and related reading

• Vue guide