docs($state): Add example on function re-binding for class methods

[webJose]

No issue to associate this with. Just adding the possibility of using bind() with class methods.

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[Rich-Harris]

preview: https://svelte-dev-git-preview-svelte-14610-svelte.vercel.app/

this is an automated message

[github-actions]

Playground

pnpm add https://pkg.pr.new/svelte@14610

[Rich-Harris]

Thank you. While this works, and is totally valid, it's actually not something we want to encourage. The reason is that while onclick={todo.reset} compiles to this...

button.__click = function (...$$args) {
  todo.reset?.apply(this, $$args);
};

...and onclick={() => todo.reset()} compiles to this...

// hoisted
var on_click = (_, todo) => todo.reset();

// in component
button.__click = [on_click, todo];

...onclick={todo.reset.bind(todo)} compiles to this:

var event_handler = $.derived(() => todo.reset.bind(todo));

button.__click = function (...$$args) {
  $.get(event_handler)?.apply(this, $$args);
};

In other words, in exchange for writing more code, we've caused the compiler to add a signal to the graph (which is unnecessary in this case, but the compiler can't know that) and generate bulkier output. Using bind made sense in the bad old days before arrow functions, but there isn't really much call for it nowadays.