Promisify WeApp API in TypeScript and preserving type.

promisify.ts

interface WxApiOpts<T, K>{
    [k: string]: any,
    success?: (callbackPayload: T) => any,
    fail?: (callbackPayload: K) => any
}

/**
 * 本方法将类似于 wx.request 等函数转化为 Promise 调用方式
 * @param callbackStyleFunction 被转换的函数，该类型函数只接受一个 Object 类型参数，且必须具备 success 和 fail 回调。
 * @param opts 防止 success 回调叫 success 的情况，传此参数进行重载。
 */
export default function <T, K>(callbackStyleFunction: (input?: WxApiOpts<T, K>) => any) {
    return function (input?: WxApiOpts<T, K>): Promise<T> {
        return new Promise((resolve: (val: T) => void, reject: (val: K) => void) => {
            let callbacks = {
                success: (res) => {
                    resolve(res);
                },
                fail: (error) => {
                    reject(error);
                }
            };
            input = input || {} as WxApiOpts<T, K>;
            let __opts = Object.assign({}, input, callbacks) as WxApiOpts<T, K>;
            callbackStyleFunction(__opts)
        });
    }
}