Comandeer/LazyPromise

'use strict';

const tmp = new WeakMap();

class LazyPromise extends Promise {
    constructor( factory ) {
        if ( typeof factory !== 'function' ) {
            throw new TypeError( `Promise resolver ${typeof factory} is not a function` );
        }

        let _resolve;
        let _reject;

        const _factory = ( resolve, reject ) => {
            _resolve = resolve;
            _reject = reject;
        };

        super( _factory );

        tmp.set( this, {
            factory,
            resolve: _resolve,
            reject: _reject
        } );
    }

    then( onSuccess, onFailure ) {
        const options = tmp.get( this );

        if ( options.factory ) {
            setImmediate( () => {
                if ( typeof options.factory === 'function' ) {
                    options.factory( options.resolve, options.reject );

                    options.factory = undefined;
                }
            } );
        }

        return super.then( onSuccess, onFailure );
    }

    catch( onFailure ) {
        return this.then( undefined, onFailure );
    }
}

module.exports = LazyPromise;