Function _createExpressionSide

src/parsetree/features/bind.js:199–225

* Create a read/write side for a parsed expression (variable, attribute, class, etc).

(expr, target, feature, runtime)

 * Create a read/write side for a parsed expression (variable, attribute, class, etc).
 */
function _createExpressionSide(expr, target, feature, runtime) {
    if (expr.type === "classRef") {
        return {
            read: function () {
                runtime.resolveAttribute(target, "class");
                return target.classList.contains(expr.className);
            },
            write: function (value) {
                if (value) {
                    target.classList.add(expr.className);
                } else {
                    target.classList.remove(expr.className);
                }
            }
        };
    }

    return {
        read: function () {
            return expr.evaluate(runtime.makeContext(target, feature, target, null));
        },
        write: function (value) {
            var ctx = runtime.makeContext(target, feature, target, null);
            _assignTo(runtime, expr, ctx, value);
        }
    };
}

/**
 * If either side wraps a form element, listen for the form's reset event