Xhr：API Cryptocurrency價格警報腳本返回錯誤和重複值

Question

這是一個簡單的vanilla JS腳本，連接到CoinMarketCap.com ticker API。

它應該做的：

1）檢索硬幣數據，將其存儲在一個對象

2）等待的時間x量（三分鐘，在這種情況下）

3 ）重複1），以獲取最新的數據

4）比較近期的數據和以前的數據

5）硬幣的價值有所回升，console.log警報

6）重複上述過程

是什麼呢： 兩個對象（firstValue和secondValue）是重複的。此外，重新開始時（再次調用main()函數），這兩個對象的內容無法上移，並顯示以前的值。

// 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(); 

爲什麼不firstValue和secondValue顯示不同的結果，即使價格已經有效地在股票變化？

請原諒任何不當使用的技術術語以及整體編碼的新手。

Answer 1

OP代碼包含許多技術和邏輯錯誤。請參閱固定代碼中的註釋。

// 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(); 

我想創建一個代碼片段，但決定不這樣做。