--- NOTE: do not edit this file, it is generated in apps/svelte.dev/scripts/sync-docs/index.ts title: export let --- In runes mode, [component props](basic-markup#Component-props) are declared with the [`$props`]($props) rune, allowing parent components to pass in data. In legacy mode, props are marked with the `export` keyword, and can have a default value: ```svelte ``` The default value is used if it would otherwise be `undefined` when the component is created. > [!NOTE] Unlike in runes mode, if the parent component changes a prop from a defined value to `undefined`, it does not revert to the initial value. Props without default values are considered _required_, and Svelte will print a warning during development if no value is provided, which you can squelch by specifying `undefined` as the default value: ```js export let foo +++= undefined;+++ ``` ## Component exports An exported `const`, `class` or `function` declaration is _not_ considered a prop — instead, it becomes part of the component's API: ```svelte ``` ```svelte ``` ## Renaming props The `export` keyword can appear separately from the declaration. This is useful for renaming props, for example in the case of a reserved word: ```svelte ```