svelte/src/validate/js/propValidators/computed.ts

import checkForDupes from '../utils/checkForDupes';
import checkForComputedKeys from '../utils/checkForComputedKeys';
import { Validator } from '../../';
import { Node } from '../../../interfaces';

const isFunctionExpression = new Set( [ 'FunctionExpression', 'ArrowFunctionExpression' ] );

export default function computed ( validator: Validator, prop: Node ) {
	if ( prop.value.type !== 'ObjectExpression' ) {
		validator.error( `The 'computed' property must be an object literal`, prop.start );
		return;
	}

	checkForDupes( validator, prop.value.properties );
	checkForComputedKeys( validator, prop.value.properties );

	prop.value.properties.forEach( ( computation: Node ) => {
		if ( !isFunctionExpression.has( computation.value.type ) ) {
			validator.error( `Computed properties can be function expressions or arrow function expressions`, computation.value.start );
			return;
		}

		const params = computation.value.params;

		if ( params.length === 0 ) {
			validator.error( `A computed value must depend on at least one property`, computation.value.start );
			return;
		}

		params.forEach( ( param: Node ) => {
			const valid = param.type === 'Identifier' || param.type === 'AssignmentPattern' && param.left.type === 'Identifier';

			if ( !valid ) {
				validator.error( `Computed properties cannot use destructuring in function parameters`, param.start );
			}
		});
	});
}