javascript - eloquent javascript 关联表 解释

Question

我正在迈出编程的第一步，但我被 Eloquent 这个问题所困扰，特别是灰鼠问题。就这样:

function hasEvent(event, entry) {
 return entry.events.indexOf(event) != -1;
}

function tableFor(event, journal) {
  var table = [0, 0, 0, 0];
   for (var i = 0; i < journal.length; i++) {
     var entry = journal[i], index = 0;
      if (hasEvent(event, entry)) index += 1;
      if (entry.squirrel) index += 2;
      table[index] += 1;
 }
 return table;
}

console.log(tableFor("pizza", JOURNAL));
// → [76, 9, 4, 1]

我确实理解第一个函数 hasevent，如果条目包含给定事件，它会返回 true。

我无法理解的是 tableFor 函数。我无法了解函数如何流动以及表如何获取其值。例如 console.log(tableFor("pizza", JOURNAL)); ，我们得到[76,9,4,1]。但看在上帝的份上怎么办？

日记由本书提供，如下所示:

var JOURNAL = [
  {"events":["pizza","exercise","weekend"],"squirrel":false},
  {"events":["bread","pudding","brushed teeth","weekend","touched 
  tree"],"squirrel":false},
  {"events":["carrot","nachos","brushed 
  teeth","cycling","weekend"],"squirrel":false},
  {"events":["brussel sprouts","ice cream","brushed 
  teeth","computer","weekend"],"squirrel":false},
  {"events":["potatoes","candy","brushed 
  teeth","exercise","weekend","dentist"],"squirrel":false},
  {"events":["brussel sprouts","pudding","brushed 
  teeth","running","weekend"],"squirrel":false},
  {"events":["pizza","brushed teeth","computer","work","touched 
  tree"],"squirrel":false},
  {"events":["bread","beer","brushed 
  teeth","cycling","work"],"squirrel":false},
  {"events":["cauliflower","brushed teeth","work"],"squirrel":false},
  {"events":["pizza","brushed teeth","cycling","work"],"squirrel":false},
  {"events":["lasagna","nachos","brushed teeth","work"],"squirrel":false},
  {"events":["brushed teeth","weekend","touched tree"],"squirrel":false},
  {"events":["lettuce","brushed 
   teeth","television","weekend"],"squirrel":false},
  {"events":["spaghetti","brushed teeth","work"],"squirrel":false},
  {"events":["brushed teeth","computer","work"],"squirrel":false},
  {"events":["lettuce","nachos","brushed teeth","work"],"squirrel":false},
  {"events":["carrot","brushed teeth","running","work"],"squirrel":false} ...etc

我的理解是，事件作为参数传递，它会查看日志中的对象数组以查看它是否存在。但计数是如何进行的呢？

if (entry.squirrel) index += 2;

为什么是+2？为什么不索引 += 3;或索引 += 4； ???

最后为什么 table[index] += 1; ???

例如，第一个循环是这样的， for : console.log(tableFor("披萨", JOURNAL));

//FLOW
i=0;

从日志上面的第一行开始，出现了披萨。

     if (hasEvent(event, entry)) index += 1;

因此索引增加并变为 1。它继续:

     if (entry.squirrel) index += 2; 

squirel 是 false，所以索引不会发生任何变化。如果找到 squirel，为什么它是 +2 ？？？

那么 表[索引] += 1从这一点上我无法理解。

有人可以帮我分解一下吗？这对我的训练会有很大帮助。

提前谢谢您。

Answer 1

table 数组是满足不同条件的条目的计数。 table[3] 是 entry.squirrel 和 hasEvent(event,entry) 都为 true 的条目的计数。 table[2] 是仅 entry.squirrel 为 true 时的计数，table[1] 是仅 hasEvent( event、entry) 为 true，table[0] 是两者都不为 true 的计数。

所以逻辑是index从0开始。如果 hasEvent(event,entry) 为 true，我们向其添加 1。如果 entry.squirrel 为 true，我们将向其添加 2。结果是，如果两者都为真，我们最终会添加 3。如果两者都不成立，我们不会添加任何内容，因此它仍然是 0。

然后我们将 1 添加到 table[index] 以增加该计数器。