javascript - 如何判断某个位置是否在特定字符之间？

Question

我用几个例子解释我的问题:

示例1:

var str = "this is a test
           and also this is a test
           and this";

范围:[19 - 22]//“也”

现在我需要检查 str 从开始到 19 的位置以及从 22 到该字符串结尾的位置是否是这个字符 $。如果存在，则返回true，否则返回false。在这种情况下，输出是:

false

<小时/>

示例2:

var str = "this $ is a test
           and also this is a test
           and this";

范围:[21 - 24]//“也”

输出:

false // there is $ before the range, but there isn't after it, so false

<小时/>

示例3:

var str = "this $ is a test
           and also this is a test
           and $this";

范围:[21 - 24]//“也”

输出:

true

<小时/>

示例4:

var str = "this $ is $ a test
           and also this is a test
           and $ this";

范围:[23 - 26]//“也”

输出:

false // there is two $ before the range and that means there isn't $ before  the range, so false

<小时/>

示例5:

var str = "this $ is $ $ a test
           and also this is a test
           and $ this";

范围:[25 - 27]//“也”

输出:

true

<小时/>

注意:我不需要使用 indexOf() 获取该范围，我已经有了这些位置。

我怎样才能做到这一点？

Answer 1

var n= str.indexOf("also");
var pre=(str.substring(0,n).match(/\$/g) || []).length;
var post=(str.substring(n+3,str.length).match(/\$/g) || []).length;
if(pre %2 ===1 && post %2===1){
console.log(true)
} else {
console.log(false);
}