Debugging

这部分主要列举了一些实际写代码过程中容易犯的错误和测试方法.

Debugging也是新版习题里新添加的内容，这一部分内容没什么难度，主要列举了一些实际写代码过程中容易犯的错误和测试方法：

• 使用console.log()来输出内容
• 当输出内容较多（如循环导致内容重复出现）时，可以使用console.clear()来清空控制台
• 可以使用typeof来测试变量的类型
• 常见错误（主要为笔误）有：
  • 变量及函数名拼写错误
  • 括号（包括中括号和大括号）及引号不完整
  • 单引号、双引号混用
  • 将赋值符=错用成等号==或===
  • 调用函数时遗漏()
  • 调用函数时传参错误（顺序错误）
  • OBOE错误（Off By One Errors)，特地查了一下，中文翻译叫差一错误，表示在使用循环时对条件的设置有偏差，导致结果多1个或少1个
  • 循环套循环时需要谨慎
  • 循环时条件设置错误导致无限循环

以上错误其实还挺容易犯的，特别是刚开始学编程的时候，比如赋值符合等号弄错，调用函数遗漏括号，这些错误我都犯过，而且可能还不止一次，其实归根到底是对知识点理解不透彻，现在回头再来学一遍基础知识，感觉查缺补漏还是很有必要的。

以下是这一部分的习题解答：

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Introduction to the Debugging Challenges

• Use the JavaScript Console to Check the Value of a Variable

  let a = 5;
  let b = 1;
  a++;
  // Add your code below this line
  console.log(a);
  
  let sumAB = a + b;
  console.log(sumAB);

• Understanding the Differences between the freeCodeCamp and Browser Console

  // Open your browser console
  let outputTwo = "This will print to the browser console 2 times";
  // Use console.log() to print the outputTwo variable
  console.log(outputTwo);
  
  let outputOne = "Try to get this to log only once to the browser console";
  // Use console.clear() in the next line to print the outputOne only once
  console.clear();
  
  // Use console.log() to print the outputOne variable
  console.log(outputOne);

• Use typeof to Check the Type of a Variable

  let seven = 7;
  let three = "3";
  console.log(seven + three);
  // Add your code below this line
  console.log(typeof seven);
  console.log(typeof three);

• Catch Misspelled Variable and Function Names

  let receivables = 10;
  let payables = 8;
  let netWorkingCapital = receivables - payables;
  console.log(`Net working capital is: ${netWorkingCapital}`);

• Catch Unclosed Parentheses, Brackets, Braces and Quotes

  let myArray = [1, 2, 3];
  let arraySum = myArray.reduce((previous, current) =>  previous + current);
  console.log(`Sum of array values is: ${arraySum}`);

• Catch Mixed Usage of Single and Double Quotes

  let innerHtml = "<p>Click here to <a href='#Home'>return home</a></p>";
  console.log(innerHtml);

• Catch Use of Assignment Operator Instead of Equality Operator

  let x = 7;
  let y = 9;
  let result = "to come";
  
  if(x === y) {
    result = "Equal!";
  } else {
    result = "Not equal!";
  }
  
  console.log(result);

• Catch Missing Open and Closing Parenthesis After a Function Call

  function getNine() {
    let x = 6;
    let y = 3;
    return x + y;
  }
  
  let result = getNine();
  console.log(result);

• Catch Arguments Passed in the Wrong Order When Calling a Function

  function raiseToPower(b, e) {
    return Math.pow(b, e);
  }
  
  let base = 2;
  let exp = 3;
  let power = raiseToPower(base, exp);
  console.log(power);

• Catch Off By One Errors When Using Indexing

  function countToFive() {
    let firstFive = "12345";
    let len = firstFive.length;
    // Fix the line below
    for (let i = 0; i < len; i++) {
    // Do not alter code below this line
      console.log(firstFive[i]);
    }
  }
  
  countToFive();

• Use Caution When Reinitializing Variables Inside a Loop

  function zeroArray(m, n) {
    // Creates a 2-D array with m rows and n columns of zeroes
    let newArray = [];
    let row = [];
    for (let j = 0; j < n; j++) {
        // Pushes n zeroes into the current row to create the columns
        row.push(0);
      }
    for (let i = 0; i < m; i++) {
      // Adds the m-th row into newArray
      // Pushes the current row, which now has n zeroes in it, to the array
      newArray.push(row);
    }
    return newArray;
  }
  
  let matrix = zeroArray(3, 2);
  console.log(matrix);

• Prevent Infinite Loops with a Valid Terminal Condition

  function myFunc() {
    for (let i = 1; i <= 4; i += 2) {
      console.log("Still going!");
    }
  }