jsonp

import { NetWorkError } from '../common/errors.js'

let jsonpId = 1;
export function jsonpCallbackId() {
    return jsonpId ++;
}

export function jsonpRequest(url, params) {
    let pStr;
    let reqUrl = url + '?' + '_=' + Date.now() + ((pStr = param2String(params)) ? '&' + pStr : '');
    return sendJsonp(reqUrl);
}

// 将键数据转换成get请求的参数形式
function param2String(params) {
    if (typeof params === 'string') {
        return params;
    }
    return objectToParamString(params);
}

// 将对象转换成键值对形式，只支持单层
function objectToParamString(params) {
    let ret = '';
    for (let key in params) {
        ret = ret + key + '=' + encodeURIComponent(params[key]) + '&';
    }
    ret = ret.substr(0, ret.length-1); // 去除最后的'&'
    return ret;
}

function sendJsonp(reqUrl) {
    return new Promise((resolve, reject)=>{
        let callbackName = 'jsonp_cb_' + jsonpCallbackId();
        let script = document.createElement('script');
        let respData = null;
        let isTimeout = false;

        let timeout = setTimeout(()=>{
            isTimeout = true;
            reject(new NetWorkError('timeout'));
        }, 5000);

        let loadCallback = ()=>{
            clearTimeout(timeout);
            if(!isTimeout) {
                respData ? resolve(respData) : reject(new NetWorkError('error'));
            }
            delete window[callbackName];
            script.removeEventListener('load', loadCallback);
            script.removeEventListener('error', loadCallback);
            document.head.removeChild(script);
        }

        script.addEventListener('load',loadCallback);
        script.addEventListener('error', loadCallback);
    
        window[callbackName] = function(resp){
            respData = resp;
        }

        script.src = reqUrl + '&callback=' + callbackName;
        document.head.appendChild(script);
    });
}

errors.js

export class NetWorkError extends Error {
    constructor(message) {
        super(message)
    
        this.errorType = 'NetWorkError'
    }
}