Question

我根本不明白这一点，有人可以解释s有什么价值吗？

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");

Answer 1

简单地说，

indexOf()方法返回字符串中第一次出现指定值的位置。

所以当我们做这样的事情时：

s = str.indexOf("o");

我们在o中找到了str的索引，并将该值重新分配到s。

你可以（而且应该）read more about the function here。

Answer 2

字符串基本上是一个字符数组，所以当你说

时

override class func shouldIncludeInDefaultSchema() -> Bool {
   return false
}

indexOf函数将其视为

str = "Hello World"

因此，如果您说[ "H", "e", "l", "l", "o", " ", "W", "o", "r", "l", "d"] 0 1 2 3 4 5 6 7 8 9 10，您将获得第一个str.indexOf('e')的索引，即1。

如果您要查找的字母不存在，该函数将返回-1。

Answer 3

//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. */

需要一些str.indexOf协助javascript

3 个答案: