bind_this() — svelte Function Reference

Source Code

packages/svelte/src/internal/client/dom/elements/bindings/this.js lines 25–61

export function bind_this(element_or_component = {}, update, get_value, get_parts) {
	effect(() => {
		/** @type {unknown[]} */
		var old_parts;

		/** @type {unknown[]} */
		var parts;

		render_effect(() => {
			old_parts = parts;
			// We only track changes to the parts, not the value itself to avoid unnecessary reruns.
			parts = get_parts?.() || [];

			untrack(() => {
				if (element_or_component !== get_value(...parts)) {
					update(element_or_component, ...parts);
					// If this is an effect rerun (cause: each block context changes), then nullify the binding at
					// the previous position if it isn't already taken over by a different effect.
					if (old_parts && is_bound_this(get_value(...old_parts), element_or_component)) {
						update(null, ...old_parts);
					}
				}
			});
		});

		return () => {
			// We cannot use effects in the teardown phase, we we use a microtask instead.
			queue_micro_task(() => {
				if (parts && is_bound_this(get_value(...parts), element_or_component)) {
					update(null, ...parts);
				}
			});
		};
	});

	return element_or_component;
}