Question

我正在浏览“开始使用Javascript”这本书，其中有一个使用while循环的示例，该循环返回单词＆＃34; Wrox＆＃34;是一个字符串。

var myString = "Welcome to Wrox books. " + 
               "The Wrox website is www.wrox.com. " + 
               "Visit the Wrox website today. Thanks for buying Wrox";

var foundAtPosition = 0;
var wroxCount = 0;

while (foundAtPosition != -1) {
    foundAtPosition = myString.indexOf("Wrox", foundAtPosition);

    if (foundAtPosition != -1) {
        wroxCount++;
        foundAtPosition++;
    }
}

document.write("There are " + wroxCount + " occurrences of the word Wrox");

不知怎的，它返回4，但似乎应该返回更高的数字。为什么wnxCount不大？像这些中的每一个都是一个事件

W - ＆gt; Wrox | wroxCount = 1

我们 - ＆gt; Wrox | wroxCount = 2

Wel - ＆gt; Wrox | wroxCount = 3

Welc - ＆gt; Wrox | wroxCount = 4

Welco - ＆gt; Wrox | wroxCount = 5

欢迎 - ＆gt; Wrox | wroxCount = 6

欢迎 - ＆gt; Wrox | wroxCount = 7

在第一个Wrox中一直到r然后在找到第二个，第三个和第四个Wrox之前表现相同。为什么wroxCount只有4？

Answer 1

您可以使用正则表达式

var myString = "Welcome to Wrox books. " + 
                   "The Wrox website is www.wrox.com. " + 
                   "Visit the Wrox website today. Thanks for buying Wrox";

alert(myString.match(/Wrox/g).length)

或者如果你想找到小写字母匹配，那么

var myString = "Welcome to Wrox books. " + 
                       "The Wrox website is www.wrox.com. " + 
                       "Visit the Wrox website today. Thanks for buying Wrox";

    alert(myString.match(/Wrox/ig).length)

Answer 2

大小写不匹配。您需要将字符串转换为相同的大小写。试试这个：

var myString = "Welcome to Wrox books. " + 
           "The Wrox website is www.wrox.com. " + 
           "Visit the Wrox website today. Thanks for buying Wrox";

var foundAtPosition = 0;
var wroxCount = 0;

while (foundAtPosition != -1) {
foundAtPosition = myString.toLowerCase().indexOf("Wrox".toLowerCase(), foundAtPosition);

if (foundAtPosition != -1) {
    wroxCount++;
    foundAtPosition++;
}
}

document.write("There are " + wroxCount + " occurrences of the word Wrox");

Answer 3

wroxCount 和的原因应该是 4是indexOf的第二个参数是起始位置

在循环的每次迭代中，起始位置设置为单词Wrox + 1的最后定位索引，因此第一次开始后每个循环开始在前一个匹配的rox位上查找单词Wrox

如果你扫描字符串，确实有四次出现Wrox这个词（wrox不匹配，因为这是区分大小写的匹配）

foundAtPosition = myString.indexOf("Wrox", foundAtPosition);

foundAtPosition将是myString中单词Wrox的索引，输入IN到indexOf函数的参数将是前一个匹配的结果（+1）

Answer 4

我认为你的程序应该返回5而不是4，但不是更高的数字。你的字符串中出现了5个单词wrox。

正如另一位回答指出的那样，你必须纠正大小写。

foundAtPosition = myString.indexOf("Wrox".toLowerCase(), foundAtPosition);

除此之外，程序按预期运行。在第一个循环中，它在整个原始字符串中搜索单词wrox。它跟踪字符串中第一次出现的位置。第二次，它再次搜索字符串。这次，搜索受限于第一次出现单词wrox直到字符串结束。然后它跟踪第二次出现的wrox。它一直这样做，直到找不到这个词为止。

关于while / indexOf（）的困惑

4 个答案: