package test;
public class Test {
    public static void main(String[] args) {
        String str = "iamhere";
        System.out.println("起始位置： " + str.indexOf("amh"));
        System.out.println("结束位置： " + (str.indexOf("amh") + "amh".length() - 1));
    }
}

运行结果：

• 起始位置： 1

• 结束位置： 3

function getSE (str, pattern) {
    const plen = pattern.length - 1,
        index = str.indexOf(pattern);
    return index === -1 ? [-1, undefined] : [index, index + plen];
}

"iamhere".match(/a/).index;
"iamhere".match(/h/).index;

str="iamhere";
target="amh";
str.match(target[target.length-1]).index;
str.match(target[0]).index;