Form Input Bindings Back

With using v-model directive, we can create two-way data bindings on form input, textarea, and select elements.

Note:

1. v-model will ignore the initial value, checked or selected attributes found on any form elements. It means that we should declare the initial value inside the data option of components.
2. For languages that require an IME (Chinese, Japanese, Korean etc.), we should use input event instead to detect the change during IME composition.

1. Basic Usages

1.1 Text

<input v-model="message" placeholder="input text" />
<p>Message is: {{ message }}</p>

1.2 Multiline Text

<textarea v-model="message" placeholder="input multiline text"></textarea>
<p>Message is: {{ message }}</p>

1.3 Checkbox

<input type="checkbox" id="checkbox" v-model="checked" />
<label for="checkbox">{{ checked }}</label>

If binding multiple checkboxes to an array:

<div id="app">
    <input type="checkbox" id="jack" value="Jack" v-model="checkedNames">
    <label for="jack">Jack</label>
    <input type="checkbox" id="john" value="John" v-model="checkedNames">
    <label for="john">John</label>
    <input type="checkbox" id="mike" value="Mike" v-model="checkedNames">
    <label for="mike">Mike</label>
    <br>
    <span>Checked names: {{ checkedNames }}</span>
</div>

const vm = new Vue({
    el: '#app',
    data: {
        checkedNames: [],
    },
});

1.4 Radio

<input type="radio" id="one" value="One" v-model="picked" />
<label for="one">One</label>
<br>
<input type="radio" id="two" value="Two" v-model="picked" />
<label for="two">Two</label>
<br>
<span>Picked: {{ picked }}</span>

1.5 Select

Single select:

<select v-model="selected">
    <option disabled value="">Please select one</option>
    <option>A</option>
    <option>B</option>
    <option>C</option>
</select>
<span>Selected: {{ selected }}</span>

Note: If the initial value of your v-model expression does not match any of the options, the <select> element will render in an "unselected" state. On iOS this will cause the user not being able to select the first item because iOS does not fire a change event in this case. It is therefore recommended to provide a disabled option with an empty value, as demonstrated in the example above.

Multiple select (bound to an array):

<select v-model="selected" multiple>
    <option>A</option>
    <option>B</option>
    <option>C</option>
</select>
<br>
<span>Selected: {{ selected }}</span>

2. Dynamic Bindings

If we need to bind value of form input items to a dynamic property, we can use v-bind to achieve that. In addition, it also allows us to bind the input value to non-string values.

2.1 Checkbox

<input
    type="checkbox"
    v-model="toggle"
    true-value="yes"
    false-value="no" />

console.log(vm.toggle); /** => yes (checked); no (unchecked) */

2.2 Select Options

<select v-model="selected">
    <!-- inline object literal -->
    <option v-bind:value="{ number: 123 }">123</option>
</select>

console.log(vm.selected.number); /** => 123 */

3. Modifiers

• .lazy

By default, v-model syncs the input with the data after each input event (except IME composition), and we can add .lazy modifier to instead sync after change event.

<!-- synced after "change" instead of "input" -->
<input v-model.lazy="msg" />

• .number

Even if specify an input element with number as its type, its returned should be string. Rather than parse with parseFloat each time, we can use .number modifier to achieve that.

<input v-model.number="age" type="number" />

• .trim

If we want to trim user input automatically, we can use .trim modifier:

<input v-model.trim="msg" />

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