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If a JavaScript regex works in the editor but fails on the published page, compare the code at each stage before blaming WordPress or the regex. Check the editor, saved post content, published page source, parsed browser DOM, and runtime value. The first stage where the text changes points to the likely cause.
Why “only the live page broke” matters
Editing, saving, rendering, and browser parsing are separate steps. A script can look correct in the editor while the saved content is sanitized, or the saved content can remain intact while a shortcode, template, theme, or plugin changes what the page emits. The browser DOM and the value JavaScript ultimately uses are further steps, not proof of what WordPress saved.
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A literal ampersand (&) inside a JavaScript regex literal is not, by itself, evidence of invalid regular-expression syntax. First inspect the exact pattern and flags. Also note whether the code uses a regex literal such as /pattern/ or constructs a pattern from a string with new RegExp(...); those are different representations to compare.
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- Copy the exact pattern from the editor. Include its delimiters and flags, and record whether it is a literal or a string passed to
RegExp. - Inspect the saved post or block content. If the pattern or its surrounding
<script>tag is already altered or missing, look at the editing surface, WordPress version, account capability, and save-time sanitization. - Open the published page’s source. Use the browser’s View Source feature and search for the exact pattern. This shows the HTML response before the browser builds its DOM. Compare it with the saved content.
- Inspect the parsed DOM and runtime value separately. If View Source has the expected text but the DOM or runtime pattern does not, investigate browser parsing, script construction, and application code. That difference does not by itself identify which one is responsible.
- Follow the output path. If a shortcode, page builder, PHP template, or other rendering layer supplies the code, inspect its returned or emitted string and filters that run afterward.
Keep the original pattern and each stage’s output side by side. The diagnosis is the earliest stage at which they differ—not necessarily the stage where the browser finally reports an error.
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When saving or editing changes the code
Custom HTML blocks and permissions
WordPress documentation says that, beginning with WordPress 7.0, the Custom HTML block has separate HTML, CSS, and JavaScript editing panels. The CSS and JavaScript panels are available only to users with the unfiltered_html capability. For users without that capability, WordPress can sanitize block content with wp_kses() on save or update, stripping disallowed markup such as <script>. Check the installed version, user capability, and block type rather than assuming the code was stored unchanged. See WordPress’s Custom HTML documentation.
Classic Editor and other editing surfaces
The Classic Editor’s visual and HTML modes handle code differently, and behavior can vary with WordPress version, editor, and plugins. Its documentation notes entity spellings such as & and &. If the code changes between editor modes or after saving, compare the stored content directly and identify which editor or builder handled it. See the WordPress Editor documentation.
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When saved content is right but the live output is not
Shortcode output
WordPress processes registered shortcodes when the_content is displayed. The shortcode handler’s returned string replaces the shortcode in the post content. If the script comes from a shortcode, inspect the callback’s return value and any later content filters. A callback that includes content is responsible for encoding or escaping it appropriately for the output context. See the Shortcode API handbook.
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Determine whether a value is being inserted as HTML text, an HTML attribute, JavaScript data, or script source. Escaping is context-specific: esc_attr() encodes ampersands and other special characters for HTML attributes such as alt, value, and title. It is not a general-purpose way to escape JavaScript source, and applying it to an entire script can produce the wrong output. See the WordPress esc_attr() reference.
Theme, plugin, and template filters
If the saved content is intact but View Source differs, inspect shortcode callbacks, template output, and theme or plugin filters that run while the page is rendered. The symptom alone does not establish that a particular plugin or theme caused it. Reproduce the issue on a staging copy and isolate the relevant filters or components there.
What WordPress’s HTML handling does—and does not—show
The WordPress HTML Tag Processor documentation treats SCRIPT contents as raw plaintext; it distinguishes them from elements such as TITLE and TEXTAREA, where character references are decoded. That is a reason to inspect the exact delivered source rather than assume an entity-looking sequence will be decoded inside script text. The documentation also describes specific safety escaping around script content, with exceptions including RegExp.prototype.source. It does not establish that WordPress generally rewrites ampersands in JavaScript regexes. See the WP_HTML_Tag_Processor reference.
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wpautop() formats paragraph breaks and may turn remaining line breaks into <br />. Its reference says line breaks inside <script>, <style>, and <svg> are not affected, so it is a weaker explanation when the specific symptom is a changed literal ampersand. See the wpautop() reference.
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| First difference appears in | Investigate next |
|---|---|
| Editor versus saved content | Editor or block type, WordPress version, user capability, and save-time sanitization. |
| Saved content versus View Source | Shortcode callback, template or PHP output, and theme or plugin filters. |
| View Source versus parsed DOM | Browser parsing and the markup surrounding the script. |
| DOM text versus runtime pattern | Script construction and application code that creates or transforms the regex. |
If the pattern works when served from a separate JavaScript file or on a minimal staging page, that comparison can help narrow the issue to the page’s content or rendering path. It does not, by itself, identify a specific filter or plugin.
What you need for a site-specific diagnosis
The symptom alone does not reveal the cause. A precise diagnosis requires the WordPress version, editing surface or builder, the user’s capability, the exact regex and flags, and the code path that emits it—such as shortcode or template code—along with the relevant theme and plugin context. Comparing the exact text at the stages above will show where to investigate without treating an ampersand or an entity spelling as proof of a regex error.
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