javascript - 请帮助理解部分JS代码

Question

我是编码和学习 indexOf() 方法的新手，我找到了这样的代码部分(见下文)我想知道为什么我们在下面的代码中使用 if() 部分。为什么没有它就不能工作？

var myString = 'Welcome to Wrox books. ';
myString = myString + 'The Wrox website is www.wrox.com. ';
myString = myString + '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');

将不胜感激任何想法。

Answer 1

您需要 if 来检查您是否找到了您要查找的字符串。 如果找不到字符串，indexOf() 将返回 -1