@thi.ng/api/mixin.js

Common, generic types, interfaces & mixins

/**
 * Class behavior mixin based on:
 * {@link http://raganwald.com/2015/06/26/decorators-in-es7.html}
 *
 * Additionally only injects/overwrites properties in target, which are NOT
 * marked with `@nomixin` (i.e. those which haven't set their `configurable`
 * property descriptor flag to `false`)
 *
 * @param behaviour - to mixin
 * @param sharedBehaviour -
 * @returns decorator function
 */
export const mixin = (behaviour, sharedBehaviour = {}) => {
    const instanceKeys = Reflect.ownKeys(behaviour);
    const sharedKeys = Reflect.ownKeys(sharedBehaviour);
    const typeTag = Symbol("isa");
    function _mixin(clazz) {
        for (let key of instanceKeys) {
            const existing = Object.getOwnPropertyDescriptor(clazz.prototype, key);
            if (!existing || existing.configurable) {
                Object.defineProperty(clazz.prototype, key, {
                    value: behaviour[key],
                    writable: true,
                });
            }
            else {
                // console.log(`not patching: ${clazz.name}.${key.toString()}`);
            }
        }
        Object.defineProperty(clazz.prototype, typeTag, { value: true });
        return clazz;
    }
    for (let key of sharedKeys) {
        Object.defineProperty(_mixin, key, {
            value: sharedBehaviour[key],
            enumerable: sharedBehaviour.propertyIsEnumerable(key),
        });
    }
    Object.defineProperty(_mixin, Symbol.hasInstance, {
        value: (x) => !!x[typeTag],
    });
    return _mixin;
};