fontoxpath/src/selectors/dataTypes/casting/castToBoolean.js

A minimalistic XPath 3.1 engine in JavaScript

import { trueBoolean, falseBoolean } from '../createAtomicValue';

/**
 * @param  {function(string):boolean}  instanceOf
 * @return {function (./AtomicValueDataType) : ({successful: boolean, value: ../AtomicValue}|{successful: boolean, error: !Error})}
 */
export default function castToBoolean (instanceOf) {
	if (instanceOf('xs:numeric')) {
		return value => ({
			successful: true,
			value: (value === 0 || isNaN(value)) ? falseBoolean : trueBoolean
		});
	}
	if (instanceOf('xs:string') || instanceOf('xs:untypedAtomic')) {
		return value => {
			switch (value) {
				case 'true':
				case '1':
					return {
						successful: true,
						value: trueBoolean
					};
				case 'false':
				case '0':
					return {
						successful: true,
						value: falseBoolean
					};
				default:
					return {
						successful: false,
						error: new Error('XPTY0004: Casting not supported from given type to xs:boolean or any of its derived types.')
					};
			}
		};
	}
	return () => ({
		successful: false,
		error: new Error('XPTY0004: Casting not supported from given type to xs:boolean or any of its derived types.')
	});
}