The general syntax is `bind:property={expression}`, where `expression` is an _lvalue_ (i.e. a variable or an object property). When the expression is an identifier with the same name as the property, we can omit the expression — in other words these are equivalent:
Svelte creates an event listener that updates the bound value. If an element already has a listener for the same event, that listener will be fired before the bound value is updated.
Most bindings are _two-way_, meaning that changes to the value will affect the element and vice versa. A few bindings are _readonly_, meaning that changing their value will have no effect on the element.
In the case of a numeric input (`type="number"` or `type="range"`), the value will be coerced to a number ([demo](/playground/untitled#H4sIAAAAAAAAE6WPwYoCMQxAfyWEPeyiOOqx2w74Hds9pBql0IllmhGXYf5dKqwiyILsLXnwwsuI-5i4oPkaUX8yo7kCnKNQV7dNzoty4qSVBSr8jG-Poixa0KAt2z5mbb14TaxA4OCtKCm_rz4-f2m403WltrlrYhMFTtcLNkoeFGqZ8yhDF7j3CCHKzpwoDexGmqCL4jwuPUJHZ-dxVcfmyYGe5MAv-La5pbxYFf5Z9Zf_UJXb-sEMquFgJJhBmGyTW5yj8lnRaD_w9D1dAKSSj7zqAQAA)):
Since 5.6.0, if an `<input>` has a `defaultValue` and is part of a form, it will revert to that value instead of the empty string when the form is reset. Note that for the initial render the value of the binding takes precedence unless it is `null` or `undefined`.
Since 5.6.0, if an `<input>` has a `defaultChecked` attribute and is part of a form, it will revert to that value instead of `false` when the form is reset. Note that for the initial render the value of the binding takes precedence unless it is `null` or `undefined`.
On `<input>` elements with `type="file"`, you can use `bind:files` to get the [`FileList` of selected files](https://developer.mozilla.org/en-US/docs/Web/API/FileList). When you want to update the files programmatically, you always need to use a `FileList` object. Currently `FileList` objects cannot be constructed directly, so you need to create a new [`DataTransfer`](https://developer.mozilla.org/en-US/docs/Web/API/DataTransfer) object and get `files` from there.
`FileList` objects also cannot be modified, so if you want to e.g. delete a single file from the list, you need to create a new `DataTransfer` object and add the files you want to keep.
> [!NOTE] `DataTransfer` may not be available in server-side JS runtimes. Leaving the state that is bound to `files` uninitialized prevents potential errors if components are server-side rendered.
A `<select>` value binding corresponds to the `value` property on the selected `<option>`, which can be any value (not just strings, as is normally the case in the DOM).
```svelte
<selectbind:value={selected}>
<optionvalue={a}>a</option>
<optionvalue={b}>b</option>
<optionvalue={c}>c</option>
</select>
```
A `<select multiple>` element behaves similarly to a checkbox group. The bound variable is an array with an entry corresponding to the `value` property of each selected `<option>`.
```svelte
<selectmultiplebind:value={fillings}>
<optionvalue="Rice">Rice</option>
<optionvalue="Beans">Beans</option>
<optionvalue="Cheese">Cheese</option>
<optionvalue="Guac (extra)">Guac (extra)</option>
</select>
```
When the value of an `<option>` matches its text content, the attribute can be omitted.
You can give the `<select>` a default value by adding a `selected` attribute to the`<option>` (or options, in the case of `<select multiple>`) that should be initially selected. If the `<select>` is part of a form, it will revert to that selection when the form is reset. Note that for the initial render the value of the binding takes precedence if it's not `undefined`.
`<video>` elements have all the same bindings as [#audio] elements, plus readonly [`videoWidth`](https://developer.mozilla.org/en-US/docs/Web/API/HTMLVideoElement/videoWidth) and [`videoHeight`](https://developer.mozilla.org/en-US/docs/Web/API/HTMLVideoElement/videoHeight) bindings.
> [!NOTE] There are [subtle differences between `innerText` and `textContent`](https://developer.mozilla.org/en-US/docs/Web/API/Node/textContent#differences_from_innertext).
> [!NOTE] `display: inline` elements do not have a width or height (except for elements with 'intrinsic' dimensions, like `<img>` and `<canvas>`), and cannot be observed with a `ResizeObserver`. You will need to change the `display` style of these elements to something else, such as `inline-block`.
To get a reference to a DOM node, use `bind:this`. The value will be `undefined` until the component is mounted — in other words, you should read it inside an effect or an event handler, but not during component initialisation:
// All instance exports are available on the instance object
export function empty() {
// ...
}
</script>
```
## bind:_property_ for components
```svelte
bind:property={variable}
```
You can bind to component props using the same syntax as for elements.
```svelte
<Keypadbind:value={pin}/>
```
While Svelte props are reactive without binding, that reactivity only flows downward into the component by default. Using `bind:property` allows changes to the property from within the component to flow back up out of the component.
let { readonlyProperty, bindableProperty = $bindable() } = $props();
</script>
```
Declaring a property as bindable means it _can_ be used using `bind:`, not that it _must_ be used using `bind:`.
Bindable properties can have a fallback value:
```svelte
<script>
let { bindableProperty = $bindable('fallback value') } = $props();
</script>
```
This fallback value _only_ applies when the property is _not_ bound. When the property is bound and a fallback value is present, the parent is expected to provide a value other than `undefined`, else a runtime error is thrown. This prevents hard-to-reason-about situations where it's unclear which value should apply.
