Write a program to count the frequency of each character in a given text file.

To count character frequencies in a text file, you would typically read the file's content into a string. Then, iterate through each character of the string. Use a hash map (or a JavaScript object) to store the counts. For each character, check if it's already a key in the map. If it is, increment its associated value (count). If not, add the character as a new key with a value of 1. Finally, the map will contain the frequency of each character.