Snippets are a useful addition to Svelte 5. I use them in my Svelte 5 projects like Edna. Snippet basics A snippet is a function that renders html based on its arguments. Here’s how to define and use a snippet: {#snippet hello(name)} <div>Hello {name}!</div> {/snippet} {@render hello("Andrew")} {@render hello("Amy")} You can re-use snippets by exporting them: <script module> export { hello }; </script> {@snippet hello(name)}<div>Hello {name}!</div>{/snippet} Snippets use cases Snippets for less nesting Deeply nested html is hard to read. You can use snippets to extract some parts to make the structure clearer. For example, you can transform: <div> <div class="flex justify-end mt-2"> <button onclick={onclose} class="mr-4 px-4 py-1 border border-black hover:bg-gray-100" >Cancel</button > <button onclick={() => emitRename()} disabled={!canRename} class="px-4 py-1 border border-black hover:bg-gray-50 disabled:text-gray-400 disabled:border-gray-400 disabled:bg-white default:bg-slate-700" >Rename</button > </div> into: {#snippet buttonCancel()} <button onclick={onclose} class="mr-4 px-4 py-1 border border-black hover:bg-gray-100" >Cancel</button > {/snippet} {#snippet buttonRename()}...{/snippet} To make this easier to read: <div> <div class="flex justify-end mt-2"> {@render buttonCancel()} {@render buttonRename()} </div> </div> snippets replace default <slot/> In Svelte 4, if you wanted place some HTML inside the component, you used <slot />. Let’s say you have Overlay.svelte component used like this: <Overlay> <MyDialog></MyDialog> </Overlay> In Svelte 4, you would use <slot /> to render children: <div class="overlay-wrapper"> <slot /> </div> <slot /> would be replaced with <MyDialog></MyDialog>. In Svelte 5 <MyDialog></MyDialog> is passed to Overlay.svelte as children property so you would change Overlay.svelte to: <script> let { children } = $props(); </script> <div class="overlay-wrapper"> {@render children()} </div> children property is created by Svelte compiler so you should avoid naming your own props children. snippets replace named slots A component can have a default slot for rendering children and additional named slots. In Svelte 5 instead of named slots you pass snippets as props. An example of Dialog.svelte: <script> let { title, children } = $props(); </script> <div class="dialog"> <div class="title"> {@render title()} </div> {@render children()} </div> And use: {#snippet title()} <div class="fancy-title">My fancy title</div> {/snippet} <Dialog title={title}> <div>Body of the dialog</div> </Dialog> passing snippets as implicit props You can pass title snippet prop implicitly: <Dialog> {#snippet title()} <div class="fancy-title">My fancy title</div> {/snippet} <div>Body of the dialog</div> </Dialog> Because {snippet title()} is a child or <Dialog>, we don’t have to pass it as explicit title={title} prop. The compiler does it for us. snippets to reduce repetition Here’s part of how I render https://tools.arslexis.io/ {#snippet row(name, url, desc)} <tr> <td class="text-left align-top" ><a class="font-semibold whitespace-nowrap" href={url}>{name}</a> </td> <td class="pl-4 align-top">{@html desc}</td> </tr> {/snippet} {@render row("unzip", "/unzip/", "unzip a file in the browser")} {@render row("wc", "/wc/", "like <tt>wc</tt>, but in the browser")} It saves me copy & paste of the same HTML and makes the structure more readable. snippets for recursive rendering Sometimes you need to render a recursive structure, like nested menus or file tree. In Svelte 4 you could use <svelte:self> but the downside of that is that you create multiple instances of the component. That means that the state is also split among multiple instances. That makes it harder to implement functionality that requires a global view of the structure, like keyboard navigation. With snippets you can render things recursively in a single instance of the component. I used it to implement nested context menus. snippets to customize rendering Let’s say you’re building a Menu component. Each menu item is a <div> with some non-trivial children. To allow the client of Menu customize how items are rendered, you could provide props for things like colors, padding etc. or you could allow ultimate flexibility by accepting an optional menuitem prop that is a snippet that renders the item. You can think of it as a headless UI i.e. you provide the necessary structure and difficult logic like keyboard navigation etc. and allow the client lots of control over how things are rendered. snippets for library of icons Before snippets every SVG Icon I used was a Svelte component. Many icons means many files. Now I have a single Icons.svelte file, like: <script module> export { IconMenu, IconSettings }; </script> {#snippet IconMenu(arg1, arg2, ...)} <svg>... icon svg</svg> {/snippet}} {#snippet IconSettings()} <svg>... icon svg</svg> {/snippet}}

SumatraPDF is a medium size (120k+ loc, not counting dependencies) Windows GUI (win32) C++ code base started by me and written by mostly 2 people. The goals of SumatraPDF are to be: fast small packed with features and yet with thoughtfully minimal UI It’s not just a matter of pride in craftsmanship of writing code. I believe being fast and small are a big reason for SumatraPDF’s success. People notice when an app starts in an instant because that’s sadly not the norm in modern software. The engineering goals of SumatraPDF are: reliable (no crashes) fast compilation to enable fast iteration SumatraPDF has been successful achieving those objectives so I’m writing up my C++ implementation decisions. I know those decisions are controversial. Maybe not Terry Davis level of controversial but still. You probably won’t adopt them. Even if you wanted to, you probably couldn’t. There’s no way code like this would pass Google review. Not because it’s bad but becaues it’s different. Diverging from mainstream this much is only feasible if you have total control: it’s your company or your own open-source project. If my ideas were just like everyone else’s ideas, there would be little point in writing about them, would it? Use UTF8 strings internally My app only runs on Windows and a string native to Windows is WCHAR* where each character consumes 2 bytes. Despite that I mostly use char* assumed to be utf8-encoded. I only decided on that after lots of code was written so it was a refactoring oddysey that is still ongoing. My initial impetus was to be able to compile non-GUI parts under Linux and Mac. I abandoned that goal but I think that’s a good idea anyway. WCHAR* strings are 2x larger than char*. That’s more memory used which also makes the app slower. Binaries are bigger if string constants are WCHAR*. The implementation rule is simple: I only convert to WCHAR* when calling Windows API. When Windows API returns WCHA* I convert it to utf-8. No exceptions Do you want to hear a joke? “Zero-cost exceptions”. Throwing and catching exceptions generate bloated code. Exceptions are a non-local control flow that makes it hard to reason about program. Every memory allocation becomes a potential leak. But RAII, you protest. RAII is a “solution” to a problem created by exceptions. How about I don’t create the problem in the first place. Hard core #include discipline I wrote about it in depth. My objects are not shy I don’t bother with private and protected. struct is just class with guts exposed by default, so I use that. While intellectually I understand the reasoning behind hiding implementation details in practices it becomes busy work of typing noise and then even more typing when you change your mind about visibility. I’m the only person working on the code so I don’t need to force those of lesser intellect to write the code properly. My objects are shy At the same time I minimize what goes into a class, especially methods. The smaller the class, the faster the build. A common problem is adding too many methods to a class. You have a StrVec class for array of strings. A lesser programmer is tempted to add Join(const char* sep) method to StrVec. A wise programmer makes it a stand-alone function: Join(const StrVec& v, const char* sep). This is enabled by making everything in a class public. If you limit visibility you then have to use friendto allow Join() function access what it needs. Another example of “solution” to self-inflicted problems. Minimize #ifdef #ifdef is problematic because it creates code paths that I don’t always build. I provide arm64, intel 32-bit and 64-bit builds but typically only develop with 64-bit intel build. Every #ifdef that branches on architecture introduces potential for compilation error which I’ll only know about when my daily ci build fails. Consider 2 possible implementations of IsProcess64Bit(): Bad: bool IsProcess64Bit() { #ifdef _WIN64 return true; #else return false; #endif } Good: bool IsProcess64Bit() { return sizeof(uintptr_t) == 8; } The bad version has a bug: it was correct when I was only doing intel builds but became buggy when I added arm64 builds. This conflicts with the goal of smallest possible size but it’s worth it. Stress testing SumatraPDF supports a lot of very complex document and image formats. Complex format require complex code that is likely to have bugs. I also have lots of files in those formats. I’ve added stress testing functionality where I point SumatraPDF to a folder with files and tell it to render all of them. For greater coverage, I also simulate some of the possible UI actions users can take like searching, switching view modes etc. Crash reporting I wrote about it in depth. Heavy use of CrashIf() C/C++ programmers are familiar with assert() macro. CrashIf() is my version of that, tailored to my needs. The purpose of assert / CrashIf is to add checks to detect incorrect use of APIs or invalid states in the program. For example, if the code tries to access an element of an array at an invalid index (negative or larger than size of the array), it indicates a bug in the program. I want to be notified about such bugs both when I test SumatraPDF and when it runs on user’s computers. As the name implies, it’ll crash (by de-referencing null pointer) and therefore generate a crash report. It’s enabled in debug and pre-release builds but not in release builds. Release builds have many, many users so I worry about too many crash reports. premake to generate Visual Studio solution Visual Studio uses XML files as a list of files in the project and build format. The format is impossible to work with in a text editor so you have no choice but to use Visual Studio to edit the project / solution. To add a new file: find the right UI element, click here, click there, pick a file using file picker, click again. To change a compilation setting of a project or a file? Find the right UI element, click here, click there, type this, confirm that. You accidentally changed compilation settings of 1 file out of a hundred? Good luck figuring out which one. Go over all files in UI one by one. In other words: managing project files using Visual Studio UI is a nightmare. Premake is a solution. It’s a meta-build system. You define your build using lua scripts, which look like test configuration files. Premake then can generate Visual Studio projects, XCode project, makefiles etc. That’s the meta part. It was truly a life server on project with lots of files (SumatraPDF’s own are over 300, many times more for third party libraries). Using /analyze and cppcheck cppcheck and /analyze flag in cl.exe are tools to find bugs in C++ code via static analysis. They are like a C++ compiler but instead of generating code, they analyze control flow in a program to find potential programs. It’s a cheap way to find some bugs, so there’s no excuse to not run them from time to time on your code. Using asan builds Address Sanitizer (asan) is a compiler flag /fsanitize=address that instruments the code with checks for common memory-related bugs like using an object after freeing it, over-writing values on the stack, freeing an object twice, writing past allocated memory. The downside of this instrumentation is that the code is much slower due to overhead of instrumentation. I’ve created a project for release build with asan and run it occasionally, especially in stress test. Write for the debugger Programmers love to code golf i.e. put us much code on one line as possible. As if lines of code were expensive. Many would write: Bad: // ... return (char*)(start + offset); I write: Good: // ... char* s = (char*)(start + offset); return s; Why? Imagine you’re in a debugger stepping through a debug build of your code. The second version makes it trivial to set a breakpoint at return s line and look at the value of s. The first doesn’t. I don’t optimize for smallest number of lines of code but for how easy it is to inspect the state of the program in the debugger. In practice it means that I intentionally create intermediary variables like s in the example above. Do it yourself standard library I’m not using STL. Yes, I wrote my own string and vector class. There are several reasons for that. Historical reason When I started SumatraPDF over 15 years ago STL was crappy. Bad APIs Today STL is still crappy. STL implementations improved greatly but the APIs still suck. There’s no API to insert something in the middle of a string or a vector. I understand the intent of separation of data structures and algorithms but I’m a pragmatist and to my pragmatist eyes v.insert (v.begin(), myarray, myarray+3); is just stupid compared to v.inert(3, el). Code bloat STL is bloated. Heavy use of templates leads to lots of generated code i.e. surprisingly large binaries for supposedly low-level language. That bloat is invisible i.e. you won’t know unless you inspect generated binaries, which no one does. The bloat is out of my control. Even if I notice, I can’t fix STL classes. All I can do is to write my non-bloaty alternative, which is what I did. Slow compilation times Compilation of C code is not fast but it feels zippy compared to compilation of C++ code. Heavy use of templates is big part of it. STL implementations are over-templetized and need to provide all the C++ support code (operators, iterators etc.). As a pragmatist, I only implement the absolute minimum functionality I use in my code. I minimize use of templates. For example Str and WStr could be a single template but are 2 implementations. I don’t understand C++ I understand the subset of C++ I use but the whole of C++ is impossibly complicated. For example I’ve read a bunch about std::move() and I’m not confident I know how to use it correctly and that’s just one of many complicated things in C++. C++ is too subtle and I don’t want my code to be a puzzle. Possibility of optimized implementations I wrote a StrVec class that is optimized for storing vector of strings. It’s more efficient than std::vector<std::string> by a large margin and I use it extensively. Temporary allocator and pool allocators I use temporary allocators heavily. They make the code faster and smaller. Technically STL has support for non-standard allocators but the API is so bad that I would rather not. My temporary allocator and pool allocators are very small and simple and I can add support for them only when beneficial. Minimize unsigned int STL and standard C library like to use size_t and other unsigned integers. I think it was a mistake. Go shows that you can just use int. Having two types leads to cast-apalooza. I don’t like visual noise in my code. Unsigned are also more dangerous. When you substract you can end up with a bigger value. Indexing from end is subtle, for (int i = n; i >= 0; i--) is buggy because i >= 0 is always true for unsigned. Sadly I only realized this recently so there’s a lot of code still to refactor to change use of size_t to int. Mostly raw pointers No std::unique_ptr for me. Warnings are errors C++ makes a distinction between compilation errors and compilation warnings. I don’t like sloppy code and polluting build output with warning messages so for my own code I use a compiler flag that turns warnings into errors, which forces me to fix the warnings.

Unexamined life is not worth living said Socrates. I don’t know about that but to become a better, faster, more productive programmer it pays to examine what makes you un-productive. Fixing bugs is one of those un-productive activities. You have to fix them but it would be even better if you didn’t write them in the first place. Therefore it’s good to reflect after fixing a bug. Why did the bug happen? Could I have done something to not write the bug in the first place? If I did write the bug, could I do something to diagnose or fix it faster? This seems like a great idea that I wasn’t doing. Until now. Here’s a random selection of bugs I found and fixed in SumatraPDF, with some reflections. SumatraPDF is a C++ win32 Windows app. It’s a small, fast, open-source, multi-format PDF/eBook/Comic Book reader. To keep the app small and fast I generally avoid using other people’s code. As a result most code is mine and most bugs are mine. Let’s reflect on those bugs. TabWidth doesn’t work A user reported that TabWidth advanced setting doesn’t work in 3.5.2 but worked in 3.4.6. I looked at the code and indeed: the setting was not used anywhere. The fix was to use it. Why did the bug happen? It was a refactoring. I heavily refactored tabs control. Somehow during the rewrite I forgot to use the advanced setting when creating the new tabs control, even though I did write the code to support it in the control. I guess you could call it sloppiness. How could I not write the bug? I could review the changes more carefully. There’s no-one else working on this project so there’s no one else to do additional code reviews. I typically do a code review by myself with webdiff but let’s face it: reviewing changes right after writing them is the worst possible time. I’m biased to think that the code I just wrote is correct and I’m often mentally exhausted. Maybe I should adopt a process when I review changes made yesterday with fresh, un-tired eyes? How could I detect the bug earlier?. 3.5.2 release happened over a year ago. Could I have found it sooner? I knew I was refactoring tabs code. I knew I have a setting for changing the look of tabs. If I connected the dots at the time, I could have tested if the setting still works. I don’t make releases too often. I could do more testing before each release and at the very least verify all advanced settings work as expected. The real problem In retrospect, I shouldn’t have implemented that feature at all. I like Sumatra’s customizability and I think it’s non-trivial contributor to it’s popularity but it took over a year for someone to notice and report that particular bug. It’s clear it’s not a frequently used feature. I implemented it because someone asked and it was easy. I should have said no to that particular request. Fix printing crash by correctly ref-counting engine Bugs can crash your program. Users rarely report crashes even though I did put effort into making it easy. When I a crash happens I have a crash handler that saves the diagnostic info to a file and I show a message box asking users to report the crash and with a press of a button I launch a notepad with diagnostic info and a browser with a page describing how to submit that as a GitHub issue. The other button is to ignore my pleas for help. Most users overwhelmingly choose to ignore. I know that because I also have crash reporting system that sends me a crash report. I get thousands of crash reports for every crash reported by the user. Therefore I’m convinced that the single most impactful thing for making software that doesn’t crash is to have a crash reporting system, look at the crashes and fix them. This is not a perfect system because all I have is a call stack of crashed thread, info about the computer and very limited logs. Nevertheless, sometimes all it takes is a look at the crash call stack and inspection of the code. I saw a crash in printing code which I fixed after some code inspection. The clue was that I was accessing a seemingly destroyed instance of Engine. That was easy to diagnose because I just refactored the code to add ref-counting to Engine so it was easy to connect the dots. I’m not a fan of ref-counting. It’s easy to mess up ref-counting (add too many refs, which leads to memory leaks or too many releases which leads to premature destruction). I’ve seen codebases where developers were crazy in love with ref-counting: every little thing, even objects with obvious lifetimes. In contrast,, that was the first ref-counted object in over 100k loc of SumatraPDF code. It was necessary in this case because I would potentially hand off the object to a printing thread so its lifetime could outlast the lifetime of the window for which it was created. How could I not write the bug? It’s another case of sloppiness but I don’t feel bad. I think the bug existed there before the refactoring and this is the hard part about programming: complex interactions between distant, in space and time, parts of the program. Again, more time spent reviewing the change could have prevented it. As a bonus, I managed to simplify the logic a bit. Writing software is an incremental process. I could feel bad about not writing the perfect code from the beginning but I choose to enjoy the process of finding and implementing improvements. Making the code and the program better over time. Tracking down a chm thumbnail crash Not all crashes can be fixed given information in crash report. I saw a report with crash related to creating a thumbnail crash. I couldn’t figure out why it crashes but I could add more logging to help figure out the issue if it happens again. If it doesn’t happen again, then I win. If it does happen again, I will have more context in the log to help me figure out the issue. Update: I did fix the crash. Fix crash when viewing favorites menu A user reported a crash. I was able to reproduce the crash and fix it. This is the bast case scenario: a bug report with instructions to reproduce a crash. If I can reproduce the crash when running debug build under the debugger, it’s typically very easy to figure out the problem and fix it. In this case I’ve recently implemented an improved version of StrVec (vector of strings) class. It had a compatibility bug compared to previous implementation in that StrVec::InsertAt(0) into an empty vector would crash. Arguably it’s not a correct usage but existing code used it so I’ve added support to InsertAt() at the end of vector. How could I not write the bug? I should have written a unit test (which I did in the fix). I don’t blindly advocate unit tests. Writing tests has a productivity cost but for such low-level, relatively tricky code, unit tests are good. I don’t feel too bad about it. I did write lots of tests for StrVec and arguably this particular usage of InsertAt() was borderline correct so it didn’t occur to me to test that condition. Use after free I saw a crash in crash reports, close to DeleteThumbnailForFile(). I looked at the code: if (!fs->favorites->IsEmpty()) { // only hide documents with favorites gFileHistory.MarkFileInexistent(fs->filePath, true); } else { gFileHistory.Remove(fs); DeleteDisplayState(fs); } DeleteThumbnailForFile(fs->filePath); I immediately spotted suspicious part: we call DeleteDisplayState(fs) and then might use fs->filePath. I looked at DeleteDisplayState and it does, in fact, deletes fs and all its data, including filePath. So we use freed data in a classic use after free bug. The fix was simple: make a copy of fs->filePath before calling DeleteDisplayState and use that. How could I not write the bug? Same story: be more careful when reviewing the changes, test the changes more. If I fail that, crash reporting saves my ass. The bug didn’t last more than a few days and affected only one user. I immediately fixed it and published an update. Summary of being more productive and writing bug free software If many people use your software, a crash reporting system is a must. Crashes happen and few of them are reported by users. Code reviews can catch bugs but they are also costly and reviewing your own code right after you write it is not a good time. You’re tired and biased to think your code is correct. Maybe reviewing the code a day after, with fresh eyes, would be better. I don’t know, I haven’t tried it.

CodeMirror 6 has @codemirror/search package which provides UI for searching within a document, triggered via Ctrl + F. In my note-taking application Edna I wanted something slightly different. This article describes how I implemented it. The UI went from: to: CodeMirror is very customizable which is great, but makes it hard to understand how to put the pieces together to achieve desired results. Almost all of the work is done in @codemirror/search, I just plugged my own UI into framework designed by the author of CodeMirror. How to get standard search UI in CodeMirror When you create CodeMirror you configure it with: import { highlightSelectionMatches, searchKeymap, } from "@codemirror/search"; EditorState.create({ // ... other stuff extensions: [ // ... other stuff highlightSelectionMatches(), keymap.of([ // ... other stuff ...searchKeymap, ]), ] }) searchKeymap is what registers key bindings like Ctrl + F to invoke search UI, F3 to find next match etc. highlightSelectionMatches is an extension that visually highlights search matches. Customizing the UI CodeMirror 6 has a notion of UI panels. Built-in search UI is a panel. Custom search UI panel Thankfully panel is as generic as it can be: it’s just a div hosting the UI. The author predicted the need for providing custom search UI so it’s as easy as adding search extension configured with custom search panel creation function: import { search, } from "@codemirror/search"; function createFindPanel() { ... } EditorState.create({ // ... other stuff extensions: [ // ... other stuff search({ createPanel: createFnddPanel, }), ] }) All the options to search() are documented here. Create the panel Function that creates the panel returns a DOM element e.g. a <div>. You can create that element using vanilla JavaScript or using a framework like Svelte, React, Vue. For Svelte the trick is to manually instantiate the component. I use Svelte 5 so I’ve created Find.svelte component which floats over the editor area thanks to position: fixed. Here’s how to manually mount it: import Find from "../components/Find.svelte"; import { mount } from "svelte"; function createFnddPanel(view) { const dom = document.createElement("div"); const args = { target: dom, props: { view, }, }; mount(Find, args); return { dom, top: true, }; } If you provide createPanel function, @codemirror/search will call it to create search UI instead of its own. It’s a great design because it reuses most of the code in @codemirror/search. The UI can be triggered programmatically, by calling openSearchPanel(EditorView) (and closed with closeSearchPanel(EditorView). Or By Mod + F key binding defined in searchKeymap. You can change the binding by not including searchKeymap and instead provide your own array of bindings to functions from @codemirror/search. By default CodeMirror shrinks the editor area to host the UI. It can host it either at the top or the bottom of the editor, which is what top return value indicates. In my case value of top doesn’t matter because my UI floats on top of editor with position: fixed and z-index: 20 so we don’t shrink the editor area. The DOM element you create is hosted within this structure: <div class="cm-panels cm-panels-top" style="top: 0px;"> <div class="cm-panel"> <!-- YOUR DOM ELEMENT --> </div> </div> My CSS provided with EditorView.theme() was: const themeBase = EditorView.theme({ ".cm-panels .cm-panel": { boxShadow: "0 0 10px rgba(0,0,0,0.15)", padding: "8px 12px", }, }); The padding made the wrapper element visible even though I didn’t want it. To fix it I simply changed it to: EditorView.theme({ ".cm-panels .cm-panel": { }, }); Doing the searches When user changes the text in input field, we need tell CodeMirror 6 to do the search. You talk to CodeMirror using those commands. To start a new search you do: let query = new SearchQuery({ search: searchTerm, replace: replaceTerm, // if you're going to run replacement commands caseSensitive: false, literal: true, }); view.dispatch({ effects: setSearchQuery.of(query), }); CodeMirror 6 supports regex search, matching case, matching only whole world option. See SearchQuery docs. To instruct CodeMirror to navigate to next, previous match etc. you call: findNext : advance to next match in the editor findPrevious : go to previous match replaceNext : replace next match replaceAll : replace all matches All those function take EditorView as an argument and act based on the last SearchQuery. All commands are documented here. Doing it in Svelte 5 Here’s the core of the component: <div class="flex"> <input bind:this={searchInput} type="text" spellcheck="false" placeholder="Find" bind:value={searchTerm} class="w-[32ch]" use:focus onkeydown={onKeyDown} /> <button onclick={next} title="find next (Enter}">next</button> <button onclick={prev} title="find previous (Shift + Enter)">prev </button> <button onclick={all} title="find all">all </button> </div> <div class="flex"> <input type="text" spellcheck="false" placeholder="Replace" bind:value={replaceTerm} class="w-[32ch]" /> <button onclick={replace}>replace</button> <button onclick={_replaceAll} class="grow">all</button> </div> We do “search as you type” by observing changes to searchTerm input field: $effect(() => { let query = new SearchQuery({ search: searchTerm, replace: replaceTerm, caseSensitive: false, literal: true, }); view.dispatch({ effects: setSearchQuery.of(query), }); }); On button press we invoke desired functionality, like: function next() { findNext(view); } Pre-populating input from selection When we show search UI it’s nice to pre-populate search term with current selection. It’s as easy as: import { getSearchQuery, } from "@codemirror/search"; let query = getSearchQuery(view.state); searchTerm = query.search; This must be done on component initialization, not in onMount(). As addition trick, we select the content of input field: onMount(() => { tick().then(() => { searchInput.select(); }); }); Closing search panel on Esc I wanted to hide search UI when Escape key is pressed. Thankfully we get searchPanelOpen(EditorView) function that tells us if search panel is open and closeSearchPanel(EditorView) to close. So it’s as easy as: function onKeyDown(ev) { if (ev.key === "Escape") { let view = getEditorView(); if (view && searchPanelOpen(view.state)) { closeSearchPanel(view); return; } } } Customizing the look of search matches CodeMirror 6 is built on web technologies so the way it allows customizing the look of things is by applying known CSS styles. You provide your own CSS to change the look of things. Here’s the CSS for search matches: <!-- this is how all matches are highlighted --> <span class="cm-searchMatch"><span class="cm-selectionMatch">another</span></span> <!-- this is how currently selected match is higlighted. It changes with findNext() / findPrevious() / selectMatches() --> <span class="cm-searchMatch cm-searchMatch-selected">another</span> How to figure things out When I started working on this I did not know any of the above. Here’s my strategy for figuring this out. Look at the source code We live in open source world. The code to @codemirror/search is available so the first step was to look at it to see exported APIs etc. Look at the docs Ok, not really. I knew so little that even though CodeMirror has extensive documentation, I just couldn’t figure out how to put the pieces together. Ask omniscient AI I saw that there is setSearchQuery API but I didn’t know how to use it. I asked Grok: how to use setSearchQuery from @codemirror/search package in codemirror 6 It gave me a good response. Look at the code again So I tried sending new SearchQuery to the editor and it didn’t work i.e. I didn’t see the matches highlighted. Back to reading the code and I see that in searchHighlighter higlight() function, it doesn’t do anything if there’s no panel. But I want my own UI, not their panel, so hmm… See how others did it Surely there must be some open source project that did something similar. The trick is to find it. I used GitHub code search to look for distinct APIs, which is harder than it looks. If you search for findNext you’ll be flooded with results. So I searched for uses of @codemirror/search. I found a few projects that created custom search UIs and that gave me enough hints on how to use the APIs and how to put all the available pieces together. Resources Edna is a note taking application for developers and power users documentation of @codemirror/search my full implementation is in Find.svelte another implementation in Vue another implementation in vanilla JavaScript