javascript - 访问数组中的数据

Question

我已经看了这个并阅读了一段时间，但似乎无法理解。我确信这很简单，但我不明白为什么我可以访问集合中的数据。我收到错误

test undefined

如果我移出 for 循环，我就可以很好地访问它。我显然缺少一些简单的东西。任何帮助都会很棒。

function whatIsInAName(collection, source) {
  // What's in a name?
  var arr = [];
  // Only change ode below this line
  var test = Object.values(source);

  for(var i = 0; i < collection.length; i++) {
    if (collection[i].test === source[0].test){
      arr[i] = collection[i];
    }
  }

  // Only change code above this line
  //arr = collection[0].last;
  return arr; 
}

whatIsInAName([{ first: "Romeo", last: "Montague" }, { first: "Mercutio", 
last: null }, { first: "Tybalt", last: "Capulet" }], { last: "Capulet" });

Answer 1

在您的代码中，Object.values 返回的是“Capulet”的 source 值，而在 for 循环中，您将 source 等同于数组(source 是对象)，这就是为什么 test 未定义

function whatIsInAName(collection, source) {
  // What's in a name?
  var arr = [];
  // Only change ode below this line
  
  
  var test = Object.keys(source);//changes values to keys
  console.log(test);
  for(var i = 0; i < collection.length; i++) {
    if (collection[i][test] === source[test]){ //change how you are accessing test
      arr.push(collection[i]);
    }
  }

  // Only change code above this line
  //arr = collection[0].last;
  console.log(arr);
  return arr; 
}

whatIsInAName([{ first: "Romeo", last: "Montague" }, { first: "Mercutio", 
last: null }, { first: "Tybalt", last: "Capulet" }], { last: "Capulet" });