coerce.ts

/**
 * Coerce decorator
 */
export function coerce<
    T extends { [key in P]: O } = any,
    P extends string | symbol = string | symbol,
    I = any,
    O = any
>(
    coerceFn: (value: I, self: T) => O,
    afterFn?: (value: O, self: T) => void
): PropertyDecorator {
    return function(target: T, propertyKey: P) {
        const _key = Symbol();
        target[_key] = target[propertyKey];
        Object.defineProperty(target, propertyKey, {
            get: function() {
                return this[_key];
            },
            set: afterFn
                ? function(v: I) {
                      this[_key] = coerceFn.call(this, v, this);
                      afterFn.call(this, this[_key], this);
                  }
                : function(v: I) {
                      this[_key] = coerceFn.call(this, v, this);
                  }
        });
    };
}