v-for Range Iteration Starts at 1, Not 0
Impact: LOW - When using v-for with a number (range iteration), the iteration starts at 1, not 0. This differs from typical JavaScript behavior where arrays are 0-indexed.
This gotcha commonly causes off-by-one errors when the generated numbers are used for calculations or array indexing.
Task Checklist
- Remember
v-for="n in 10"produces 1 through 10, not 0 through 9 - When using range values for array indexing, subtract 1:
items[n - 1] - Consider creating a computed array if you need 0-based indices
Incorrect Assumption:
<!-- Developer expects 0-9, but gets 1-10 -->
<span v-for="n in 10">{{ n }}</span>
<!-- Output: 1 2 3 4 5 6 7 8 9 10 -->
<!-- WRONG: Off-by-one error when used for array access -->
<li v-for="n in items.length" :key="n">
{{ items[n].name }} <!-- Error! items[10] is undefined when length is 10 -->
</li>Correct:
<!-- Correct understanding: 1-based range -->
<span v-for="n in 10" :key="n">{{ n }}</span>
<!-- Output: 1 2 3 4 5 6 7 8 9 10 -->
<!-- CORRECT: Adjust index for array access -->
<li v-for="n in items.length" :key="n">
{{ items[n - 1].name }} <!-- n-1 converts to 0-based -->
</li>
<!-- BETTER: Just iterate the array directly -->
<li v-for="(item, index) in items" :key="item.id">
{{ index + 1 }}. {{ item.name }} <!-- index is 0-based, add 1 for display -->
</li><!-- Range for repeating elements (no array involved) -->
<div v-for="n in 3" :key="n" class="skeleton-row">
Loading placeholder {{ n }} of 3...
</div>
<!-- Output: Loading placeholder 1 of 3, 2 of 3, 3 of 3 -->When Range Iteration Is Useful
- Rendering a fixed number of placeholder/skeleton elements
- Creating pagination buttons:
v-for="page in totalPages" - Generating star ratings:
v-for="star in 5" - Repeating template structures a set number of times