charging-cabinet/software/h5-uniapp/.agents/skills/vue-best-practices/reference/v-model-number-modifier-behavior.md

title, impact, impactDescription, type, tags

title	impact	impactDescription	type	tags
v-model.number Uses parseFloat Not valueAsNumber	MEDIUM	.number modifier returns empty string for empty input and uses parseFloat, not native valueAsNumber	capability	vue3 v-model forms input number type-coercion modifiers

v-model.number Uses parseFloat Not valueAsNumber

Impact: MEDIUM - The .number modifier doesn't behave like the native valueAsNumber property. It returns an empty string (not NaN) for empty inputs, and uses parseFloat() which has different parsing rules. This can cause unexpected type issues in calculations and validations.

Understanding these differences is crucial when working with numeric forms, especially for calculations, min/max validation, or when interfacing with APIs that expect strict number types.

Task Checklist

• Expect empty string (not 0 or NaN) when input is cleared with .number modifier
• Handle the empty string case in your validation and calculations
• Remember .number uses parseFloat - "123abc" becomes 123, not NaN
• For strict numeric parsing, add custom validation

Key Differences:

Scenario	.number modifier	Native valueAsNumber
Empty input	'' (empty string)	NaN
"123"	123	123
"123.45"	123.45	123.45
"123abc"	123	NaN
"abc"	'abc' (original string)	NaN

Problem - Unexpected types:

<script setup>
import { ref, computed } from 'vue'

const price = ref(0)
const quantity = ref(1)

const total = computed(() => {
  // PROBLEM: price might be '' (empty string) when input is cleared
  return price.value * quantity.value  // '' * 1 = 0, but typeof is still number
})

function validatePrice() {
  // PROBLEM: This check fails when input is empty
  if (typeof price.value !== 'number') {
    // Never enters here! '' is still treated as "processed"
  }

  // PROBLEM: parseFloat("$100") returns NaN, but "100abc" returns 100
}
</script>

<template>
  <input v-model.number="price" type="number">
  <!-- When user clears input, price.value becomes '' not 0 or NaN -->
</template>

Solution - Handle empty string explicitly:

<script setup>
import { ref, computed } from 'vue'

const price = ref(0)
const quantity = ref(1)

const total = computed(() => {
  // CORRECT: Handle empty string case
  const priceNum = price.value === '' ? 0 : price.value
  return priceNum * quantity.value
})

// Or use a wrapper computed for safer access
const safePrice = computed(() => {
  if (price.value === '' || price.value === null) return 0
  return Number(price.value) || 0
})
</script>

<template>
  <input v-model.number="price" type="number" min="0">
  <p>Total: ${{ total.toFixed(2) }}</p>
</template>

Solution - Custom input handling for strict parsing:

<script setup>
import { ref } from 'vue'

const price = ref(0)

function handlePriceInput(event) {
  const value = event.target.value

  // Strict parsing - only accept valid numbers
  const parsed = parseFloat(value)

  if (value === '') {
    price.value = 0  // Or null, depending on your needs
  } else if (!isNaN(parsed) && isFinite(parsed)) {
    // Additional check: ensure entire string is numeric
    if (/^-?\d*\.?\d+$/.test(value.trim())) {
      price.value = parsed
    }
  }
  // Invalid input - keep previous value
}
</script>

<template>
  <!-- Manual binding for strict numeric control -->
  <input
    :value="price"
    @input="handlePriceInput"
    type="number"
  >
</template>

Reference

• Vue.js Form Input Bindings - .number