character questions

`String.prototype.charAt` returns the character at a specified index in a string. If the index is out of range, it returns an empty string. 

const str = 'hello';
const char = str.charAt(1);
console.log(char); // 'e'

Use a hash map to count the frequency of each character, then iterate through the string to find the first character with a count of 1. For example, in 'swiss', the first non-repeating character is 'w'.

XML has several key features: 1. Simplicity: It is easy to understand and read. 2. Extensibility: You can define your own tags. 3. Structure: Data is stored in a hierarchical format. 4. Platform independent: It can be used across different systems. 5. Human and machine-readable: XML is easily readable by both humans and machines. 6. Self-descriptive: Tags describe the data they enclose. 

 <person>
  <name>John</name>
  <age>30</age>
</person>