描述
Migrate jQuery 3.x to 4.0.0 safely in WordPress and legacy web projects. Covers all breaking changes: removed APIs ($.isArray, $.trim, $.parseJSON, $.type), focus event order changes, slim build differences, ES modules migration, and Trusted Types support. Use when: upgrading jQuery to 4.0, fixing "$.isArray is not a function" errors, WordPress jQuery migration, updating legacy JavaScript, or troubleshooting focus/blur event order issues.