Xhr：API Cryptocurrency价格警报脚本返回错误和重复值

Question

这是一个简单的vanilla JS脚本，连接到CoinMarketCap.com ticker API。

它应该做的：

1）检索硬币数据，将其存储在一个对象

2）等待的时间x量（三分钟，在这种情况下）

3 ）重复1），以获取最新的数据

4）比较近期的数据和以前的数据

5）硬币的价值有所回升，console.log警报

6）重复上述过程

是什么呢： 两个对象（firstValue和secondValue）是重复的。此外，重新开始时（再次调用main()函数），这两个对象的内容无法上移，并显示以前的值。

// Variables 

// Set first recorded value 
var firstValue; 

// Set second value (most recent) 
var secondValue; 


// Get the obj from CoinMarketCap API 
function getCoinValues() { 
    var requestURL ="https://api.coinmarketcap.com/v1/ticker/?limit=10"; 
    var request = new XMLHttpRequest(); 
    request.open("GET", requestURL); 
    request.send(); 

    // When loaded assign to obj variable and return it 
    request.onload = function getUsdValues() { 
     // Save data to the 'obj' object 
     obj = JSON.parse(request.response); 
     console.log("Retrieved coin data"); 
     }; 
    return obj; 
} 


// Wait 
function wait(ms){ 
    console.log("Waiting.") 
    var start = new Date().getTime(); 
    var end = start; 
    while(end < start + ms) { 
    end = new Date().getTime(); 
    }   
} 


// Compare two objects 
function comparePrices (obj1, obj2) { 
    // Take price from one array, compare to the other 
    for (var i = 0; i < obj1.length; i++) { 
      // console.log(JSON.stringify(obj2[i].id) + " OLD:" + obj1[i].price_usd + "NEW:" + obj2[i].price_usd) 
      if (obj2[i].price_usd > obj1[i].price_usd) { 
       console.log(JSON.stringify(obj2[i].id) + " has increased!"); 
       console.log("From $" + obj1[i].price_usd + " to $" + obj2[i].price_usd); 

      } 
     } 

} 


// Main function // 

function main() { 
    // Get 1st coin values 
    console.log("Getting first values"); 
    firstValue = getCoinValues(); 

    // Wait 
    console.log("Waiting") 
    wait(30000); 

    // Retrieve new values 
    console.log("Getting second values") 
    secondValue = getCoinValues(); 

    // Compare two sets of values 
    console.log("About to compare prices") 
    comparePrices(firstValue, secondValue); 
    console.log("Prices compared") 

    // Do it all again 

    // "Emptying" the variables 
    firstValue = null 
    secondValue = null 

    // Starting the main loop 
    main(); 

} 

main(); 

为什么不firstValue和secondValue显示不同的结果，即使价格已经有效地在股票变化？

请原谅任何不当使用的技术术语以及整体编码的新手。

Answer 1

OP代码包含许多技术和逻辑错误。请参阅固定代码中的注释。

// Variables 

// Set first recorded value 
//var firstValue; //no use 

// Set second value (most recent) 
//var secondValue; //no use 

//Save AJAX response here 
var currentValue = []; 
//define the const URL 
var requestURL = "https://api.coinmarketcap.com/v1/ticker/?limit=10"; 

// Get the obj from CoinMarketCap API - wrong description 
//Process request to API 
function getCoinValues() { 
    //var requestURL = "https://api.coinmarketcap.com/v1/ticker/?limit=10"; 
    var request = new XMLHttpRequest(); 
    request.open("GET", requestURL); 
    //request.send();//dedine a handler first 
    request.onreadystatechange = function() { 
     if (this.readyState == 4 && this.status == 200) { //**this** is request 
      var tmpObj = JSON.parse(this.responseText); 
      if (currentValue && tmpObj) {//compare when both arrays exist 
       comparePrices(currentValue, tmpObj); 
      } 
      if (tmpObj) //response received and parsed 
       currentValue = tmpObj; 
      //console.log(tmpObj); 
     } 
    } 
    //now it is good time to send request 
    request.send(); 

    // When loaded assign to obj variable and return it 
    //request.onload = function getUsdValues() { 
    // // Save data to the 'obj' object 
    // obj = JSON.parse(request.response); //obj was never defined 
    // console.log("Retrieved coin data"); 
    //}; 
    //return obj; //never try to return anything from asynchronous function 
} 


// Wait 
//Good to hang the system 
/* 
function wait(ms) { 
    console.log("Waiting.") 
    var start = new Date().getTime(); 
    var end = start; 
    while (end < start + ms) { 
     end = new Date().getTime(); 
    } 
} 
*/ 

// Compare two objects (arrays in fact) 
function comparePrices(obj1, obj2) { //usage: comparePrices(current,new) 
    console.log(new Date().toLocaleTimeString()); 
    // Take price from one array, compare to the other 
    for (var i = 0; i < obj1.length; i++) { 
     // console.log(JSON.stringify(obj2[i].id) + " OLD:" + obj1[i].price_usd + "NEW:" + obj2[i].price_usd) 
     if (obj2[i].price_usd > obj1[i].price_usd) { 
      //console.log(JSON.stringify(obj2[i].id) + " has increased!"); //no need to stringify. 
      console.log(obj2[i].id + " has increased! From $" + obj1[i].price_usd + " to $" + obj2[i].price_usd); 
     } else if (obj2[i].price_usd < obj1[i].price_usd) { 
      console.log(obj2[i].id + " has decreased! From $" + obj1[i].price_usd + " to $" + obj2[i].price_usd); 
     } else { 
      console.log(obj2[i].id + " No change $" + obj2[i].price_usd); 
     } 
    } 
} 

// Main function // 

function main() { 
    getCoinValues(); 
    setTimeout(main, 30000);//run again in 30 sec 
    return; 
    //All remaining code is wrong 

    //// Get 1st coin values 
    //console.log("Getting first values"); 
    //firstValue = getCoinValues(); 

    //// Wait 
    //console.log("Waiting") 
    //wait(30000); 

    //// Retrieve new values 
    //console.log("Getting second values") 
    //secondValue = getCoinValues(); 

    //// Compare two sets of values 
    //console.log("About to compare prices") 
    //comparePrices(firstValue, secondValue); 
    //console.log("Prices compared") 

    //// Do it all again 

    //// "Emptying" the variables 
    //firstValue = null 
    //secondValue = null 

    //// Starting the main loop 
    //main(); 

} 

main(); 

我想创建一个代码片段，但决定不这样做。