Gutenberg Custom Block Getting All Posts

In addition to loading the wp-api script as mentioned here:

wp_enqueue_script( 'wp-api' ); // or use below when enqueueing as dependency
//wp_enqueue_script( 'my_script', 'path/to/my/script', array( 'wp-api' ) );

You should also know that each collection is a function (equivalent to a class in PHP), so you need to use the new keyword to instantiate a collection. Example:

var postsCollection = new wp.api.collections.Posts();
postsCollection.fetch( {
    data: { per_page: 2 }
} ).done( function( posts ){
    console.log( 'Title of the first item is: ' + posts[0].title.rendered );
} );

However, with Gutenberg, you’d likely want to or you can use the api-fetch/wp.apiFetch package:

1. Enqueue the wp-api-fetch script:

   wp_enqueue_script( 'wp-api-fetch' ); // or use below when enqueueing as dependency
   //wp_enqueue_script( 'my_script', 'path/to/my/script', array( 'wp-api-fetch' ) );
   

2. And just call wp.apiFetch() like so:

   wp.apiFetch( { path: '/wp/v2/posts?per_page=2' } ).then( function( posts ){
       console.log( 'Title of the first item is: ' + posts[0].title.rendered );
   } );
   

   path is a REST API route like /wp/v2/posts which can optionally be appended with one or more arguments for that specific route.

How can I get a list of all the posts for selection within the editor

If you’re on the admin screen for editing or creating a post, then the wp-api-fetch script has already been enqueued if the block editor is enabled for that post. And if you’re specifically creating a block, then you can actually use getEntityRecords() along with withSelect (for listening to state changes). See the Latest Posts block for sample implementation.