build_expression() — svelte Function Reference

Architecture documentation for the build_expression() function in utils.js from the svelte codebase.

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Compiler→ Transformer→ build_expression() — svelte Function Reference

Dependency Diagram

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  e31bc2c2_91c1_b9a9_f78a_2832bddce6c5["build_attribute_value()"]
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  f3280f06_553d_66c3_8ca2_c3c36dcdda64["build_template_chunk()"]
  f3280f06_553d_66c3_8ca2_c3c36dcdda64 -->|calls| 66243dec_e2be_a66d_3992_3ea42cf964b5
  27fded45_bc11_247b_d3fe_94831379f9ed["build_getter()"]
  66243dec_e2be_a66d_3992_3ea42cf964b5 -->|calls| 27fded45_bc11_247b_d3fe_94831379f9ed
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Relationship Graph

Source Code

packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/utils.js lines 442–482

export function build_expression(context, expression, metadata, state = context.state) {
	const value = /** @type {Expression} */ (context.visit(expression, state));

	// Components not explicitly in legacy mode might be expected to be in runes mode (especially since we didn't
	// adjust this behavior until recently, which broke people's existing components), so we also bail in this case.
	// Kind of an in-between-mode.
	if (context.state.analysis.runes || context.state.analysis.maybe_runes) {
		return value;
	}

	if (!metadata.has_call && !metadata.has_member_expression && !metadata.has_assignment) {
		return value;
	}

	// Legacy reactivity is coarse-grained, looking at the statically visible dependencies. Replicate that here
	const sequence = b.sequence([]);

	for (const binding of metadata.references) {
		if (binding.kind === 'normal' && binding.declaration_kind !== 'import') {
			continue;
		}

		var getter = build_getter({ ...binding.node }, state);

		if (
			binding.kind === 'bindable_prop' ||
			binding.kind === 'template' ||
			binding.declaration_kind === 'import' ||
			binding.node.name === '$$props' ||
			binding.node.name === '$$restProps'
		) {
			getter = b.call('$.deep_read_state', getter);
		}

		sequence.expressions.push(getter);
	}

	sequence.expressions.push(b.call('$.untrack', b.thunk(value)));

	return sequence;
}