PHP’s htmlspecialchars Implemented in JavaScript

htmlspecialchars is an extremely useful PHP function. Its use is defined by the PHP manual as such:

Certain characters have special significance in HTML, and should be represented by HTML entities if they are to preserve their meanings. This function returns a string with some of these conversions made; the translations made are those most useful for everyday web programming…

This function is useful in preventing user-supplied text from containing HTML markup, such as in a message board or guest book application.