Add escapeHtml function for HTML context escaping

[pavankumar-vh]

Overview

Add a dedicated escapeHtml function for escaping strings in HTML contexts, separate from the existing escapeString function.

Problem

The previous PR (#1231) modified escapeString to escape HTML-unsafe characters, but this could break existing callers that depend on the un-escaped characters passing through (e.g., building strings for JSON parsing or non-HTML contexts).

Fix

Added a separate escapeHtml function that explicitly escapes HTML-unsafe characters (<, >, &, ') to prevent XSS attacks and HTML injection. The existing escapeString function remains unchanged for backward compatibility.

export const escapeHtml = (str: string): string => {
  return JSON.stringify(str)
    .slice(1, -1)
    .replace(/</g, '\\u003c')
    .replace(/>/g, '\\u003e')
    .replace(/&/g, '\\u0026')
    .replace(/'/g, '\\u0027')
}

Testing

Added comprehensive test coverage for both functions:

• escapeString tests verify it still escapes JSON special characters but NOT HTML-unsafe ones
• escapeHtml tests verify it properly escapes <script>, &, ', > to prevent XSS
• Both functions tested with empty strings and regular characters

All 24 tests pass (19 existing + 5 new).

Files Changed

• common/src/util/string.ts - Added escapeHtml function
• common/src/util/__tests__/string.test.ts - Added test coverage for both functions

Scope

This change only touches common/ which is an approved contribution area per the Contributing Guide.