需要一些str.indexOf帮助javascript

need some str.indexOf assistance javascript

本文关键字：indexOf 帮助 javascript str      更新时间：2023-09-26

我一点都不明白，有人能解释一下s是如何有值的吗？

var str="Hello World"
// What is the value of s after each line is executed?
s = str.indexOf("o");
s = str.indexOf("w");
s = str.indexOf("r");
s = str.lastIndexOf("l");

简单地说，

indexOf()方法返回字符串中指定值第一次出现的位置。

所以当我们做这样的事情时：

s = str.indexOf("o");

我们在str中找到o的索引，并将该值赋值回s。

你可以（也应该）在这里阅读更多关于这个函数的信息。

字符串基本上是一个字符数组，所以当你说时

str = "Hello World"

indexOf函数将其视为

[ "H", "e", "l", "l", "o", " ", "W", "o", "r", "l", "d"]
   0    1    2    3    4    5    6    7    8    9   10

所以如果你说str.indexOf('e')，你会得到第一个e的索引，它是1。

如果您要查找的字母不存在，函数将返回-1。

//The 'indexOf()' method returns an integer value that states the position (startig from 0) of the first occurrence of the value of the parameter passed.
//Now, 
var str="Hello World"
s = str.indexOf("o");
console.log(s);
/* This would give an output 4. As you can see, 'o' is the fifth character in the String. If you start from 0, the position is 4. */
s = str.indexOf("w");
console.log(s);
/* This would give an output -1. As you can see 'w' doesn't exist in str. If the required value is not found, the function returns -1. */
s = str.indexOf("r");
console.log(s);
/* This would give an output 8. Why? Refer to the explanation for the first function. */
s = str.lastIndexOf("l");
console.log(s);
/* This would give an output 9. This gives the position of the last occurence of the value of parameter passed. */
/* How s has a value? Because the function returns a value that is assigned to s by '=' operator. */
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