--- NOTE: do not edit this file, it is generated in apps/svelte.dev/scripts/sync-docs/index.ts title: bind: --- Data ordinarily flows down, from parent to child. The `bind:` directive allows data to flow the other way, from child to parent. The general syntax is `bind:property={expression}`, where `expression` is an [_lvalue_](https://press.rebus.community/programmingfundamentals/chapter/lvalue-and-rvalue/) (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 ``` 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. ## Function bindings You can also use `bind:property={get, set}`, where `get` and `set` are functions, allowing you to perform validation and transformation: ```svelte value, (v) => value = v.toLowerCase()} /> ``` In the case of readonly bindings like [dimension bindings](#Dimensions), the `get` value should be `null`: ```svelte

...

``` > [!NOTE] > Function bindings are available in Svelte 5.9.0 and newer. ## `` A `bind:value` directive on an `` element binds the input's `value` property: ```svelte

{message}

``` 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)): ```svelte

{a} + {b} = {a + b}

``` If the input is empty or invalid (in the case of `type="number"`), the value is `undefined`. Since 5.6.0, if an `` 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`. ```svelte ``` > [!NOTE] > Use reset buttons sparingly, and ensure that users won't accidentally click them while trying to submit the form. ## `` Checkbox inputs can be bound with `bind:checked`: ```svelte Accept terms and conditions ``` Since 5.6.0, if an `` 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`. ```svelte ``` > [!NOTE] Use `bind:group` for radio inputs instead of `bind:checked`. ## `` Checkboxes can be in an [indeterminate](https://developer.mozilla.org/en-US/docs/Web/API/HTMLInputElement/indeterminate) state, independently of whether they are checked or unchecked: ```svelte ``` ## `` Inputs that work together can use `bind:group` ([demo](/playground/untitled#H4sIAAAAAAAAE62T32_TMBDH_5XDQkpbrct7SCMGEvCEECDxsO7BSW6L2c227EvbKOv_jp0f6jYhQKJv5_P3PvdL1wstH1Bk4hMSGdgbRzUssFaM9VJciFtF6EV23QvubNRFR_BPUVfWXvodEkdfKT3-zl8Zzag5YETuK6csF1u9ZUIGNo4VkYQNvPYsGRfJF5JKJ8s3QRJE6WoFb2Nq6K-ck13u2Sl9Vxxhlc6QUBIFnz9Brm9ifJ6esun81XoNd860FmtwslYGlLYte5AO4aHlVhJ1gIeKWq92COt1iMtJlkhFPkgh1rHZiiF6K6BUus4G5KafGznCTlIbVUMfQZUWMJh5OrL-C_qjMYSwb1DyiH7iOEuCb1ZpWTUjfHqcwC_GWDVY3ZfmME_SGttSmD9IHaYatvWHIc6xLyqad3mq6KuqcCwnWn9p8p-p71BqP2IH81zc9w2in-od7XORP7ayCpd5YCeXI_-p59mObPF9WmwGpx3nqS2Gzw8TO3zOaS5_GqUXyQUkS3h8hOSz0ZhMESHGc0c4Hm3MAn00t1wrb0l2GZRkqvt4sXwczm6Qh8vnUJzI2LV4vAkvqWgfehTZrSSPx19WiVfFfAQAAA==)): ```svelte Plain Whole wheat Spinach Rice Beans Cheese Guac (extra) ``` > [!NOTE] `bind:group` only works if the inputs are in the same Svelte component. ## `` On `` 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. ```svelte Upload a picture: ``` `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. ## `` value binding corresponds to the `value` property on the selected ` ``` When the value of an ` ``` ## `