Synchronise caret/placeholder color

code-input.css

@@ -20,7 +20,14 @@ code-input {
   top: 0;
   left: 0;
 
-  color: black;
+  /* CSS variables rather than inline styles used for values synced from JavaScript
+   to keep low precedence and thus overridability
+   The variable names may change and are for internal use. */
+  /* --code-input_highlight-text-color: Set by JS to be base text color of pre code element */
+  /* --code-input_no-override-color: Set by JS for very short time to get whether color has been overriden */
+  color: var(--code-input_no-override-color, black);
+  /* --code-input_default-caret-color: Set by JS to be same as color property - currentColor won't work because it's lazily evaluated so gives transparent for the textarea */
+  caret-color: var(--code-input_default-caret-color, inherit);
   background-color: white;
 
   /* Normal inline styles */
@@ -36,7 +43,6 @@ code-input {
   text-align: start;
   line-height: 1.5; /* Inherited to child elements */
   tab-size: 2;
-  caret-color: darkgrey;
   white-space: pre;
   padding: 0!important; /* Use --padding to set the code-input element's padding */
   display: grid;
@@ -68,6 +74,12 @@ code-input textarea, code-input:not(.code-input_pre-element-styled) pre code, co
 code-input:not(.code-input_pre-element-styled) pre code, code-input.code-input_pre-element-styled pre {
   height: max-content;
   width: max-content;
+
+
+  /* Allow colour change to reflect properly;
+  transition-behavior: allow-discrete could be used but this is better supported and
+  works with the color property. */
+  transition: color 0.001s;
 }
 
 code-input:not(.code-input_pre-element-styled) pre, code-input.code-input_pre-element-styled pre code {
@@ -118,12 +130,13 @@ code-input pre {
 /* Make textarea almost completely transparent, except for caret and placeholder */
 
 code-input textarea:not([data-code-input-fallback]) {
-  color: transparent;
   background: transparent;
-  caret-color: inherit!important; /* Or choose your favourite color */
+  color: transparent;
+  caret-color: inherit;
 }
-code-input textarea::placeholder {
-  color: lightgrey;
+code-input textarea:not([data-code-input-fallback]):placeholder-shown {
+  /* Show placeholder */
+  color: var(--code-input_highlight-text-color, inherit);
 }
 
 /* Can be scrolled */
@@ -163,6 +176,11 @@ code-input .code-input_dialog-container {
 
   /* Dialog boxes' text is based on text-direction */
   text-align: inherit;
+
+  /* Allow colour change to reflect properly;
+   * transition-behavior: allow-discrete could be used but this is * better supported and works with the color property. */
+  color: inherit;
+  transition: color 0.001s;
 }
 
 [dir=rtl] code-input .code-input_dialog-container, code-input[dir=rtl] .code-input_dialog-container {
@@ -252,11 +270,13 @@ code-input:not(.code-input_loaded) pre, code-input:not(.code-input_loaded) texta
 code-input:has(textarea[data-code-input-fallback]) {
   padding: 0!important; /* Padding now in the textarea */
   box-sizing: content-box;
+
+  caret-color: revert; /* JS not setting the colour since no highlighting */
 }
 code-input textarea[data-code-input-fallback] {
   overflow: auto;
   background-color: inherit;
-  color: inherit;
+  color: var(--code-input_highlight-text-color, inherit);
 
   /* Don't overlap with message */
   min-height: calc(100% - var(--padding-top, 16px) - 2em - var(--padding-bottom, 16px));

code-input.js

@@ -152,6 +152,8 @@ var codeInput = {
         }
     },
 
+    stylesheetI: 0, // Increments to give different classes to each code-input element so they can have custom styles synchronised internally without affecting the inline style
+
     /**
      * Please see `codeInput.templates.prism` or `codeInput.templates.hljs`.
      * Templates are used in `<code-input>` elements and once registered with
@@ -445,6 +447,16 @@ var codeInput = {
          */
         dialogContainerElement = null;
 
+        /**
+         * Like style attribute, but with a specificity of 1
+         * element, 1 class. Present so styles can be set on only
+         * this element while giving other code freedom of use of
+         * the style attribute.
+         *
+         * For internal use only.
+         */
+        internalStyle = null;
+
         /**
         * Form-Associated Custom Element Callbacks
         * https://html.spec.whatwg.org/multipage/custom-elements.html#custom-elements-face-example
@@ -530,22 +542,75 @@ var codeInput = {
             this.pluginEvt("afterHighlight");
         }
 
+        getStyledHighlightingElement() {
+            if(this.templateObject.preElementStyled) {
+                return this.preElement;
+            } else {
+                return this.codeElement;
+            }
+        }
+
         /**
          * Set the size of the textarea element to the size of the pre/code element.
          */
         syncSize() {
             // Synchronise the size of the pre/code and textarea elements
-            if(this.templateObject.preElementStyled) {
-                this.style.backgroundColor = getComputedStyle(this.preElement).backgroundColor;
-                this.textareaElement.style.height = getComputedStyle(this.preElement).height;
-                this.textareaElement.style.width = getComputedStyle(this.preElement).width;
-            } else {
-                this.style.backgroundColor = getComputedStyle(this.codeElement).backgroundColor;
-                this.textareaElement.style.height = getComputedStyle(this.codeElement).height;
-                this.textareaElement.style.width = getComputedStyle(this.codeElement).width;
+            this.textareaElement.style.height = getComputedStyle(this.getStyledHighlightingElement()).height;
+            this.textareaElement.style.width = getComputedStyle(this.getStyledHighlightingElement()).width;
+        }
+
+        /**
+         * If the color attribute has been defined on the
+         * code-input element by external code, return true.
+         * Otherwise, make the aspects the color affects
+         * (placeholder and caret colour) be the base colour
+         * of the highlighted text, for best contrast, and
+         * return false.
+         */
+        isColorOverridenSyncIfNot() {
+            const oldTransition = this.style.transition;
+            this.style.transition = "unset";
+            window.requestAnimationFrame(() => {
+                this.internalStyle.setProperty("--code-input_no-override-color", "rgb(0, 0, 0)");
+                if(getComputedStyle(this).color == "rgb(0, 0, 0)") {
+                    // May not be overriden
+                    this.internalStyle.setProperty("--code-input_no-override-color", "rgb(255, 255, 255)");
+                    if(getComputedStyle(this).color == "rgb(255, 255, 255)") {
+                        // Definitely not overriden
+                        this.internalStyle.removeProperty("--code-input_no-override-color");
+                        this.style.transition = oldTransition;
+
+                        const highlightedTextColor = getComputedStyle(this.getStyledHighlightingElement()).color;
+
+                        this.internalStyle.setProperty("--code-input_highlight-text-color", highlightedTextColor);
+                        this.internalStyle.setProperty("--code-input_default-caret-color", highlightedTextColor);
+                        return false;
+                    }
+                }
+                this.internalStyle.removeProperty("--code-input_no-override-color");
+                this.style.transition = oldTransition;
+            });
+
+            return true;
+        }
+
+        /**
+         * Update the aspects the color affects
+         * (placeholder and caret colour) to the correct
+         * colour: either that defined on the code-input
+         * element, or if none is defined externally the
+         * base colour of the highlighted text.
+         */
+        syncColorCompletely() {
+            // color of code-input element
+            if(this.isColorOverridenSyncIfNot()) {
+                // color overriden
+                this.internalStyle.removeProperty("--code-input_highlight-text-color");
+                this.internalStyle.setProperty("--code-input_default-caret-color", getComputedStyle(this).color);
             }
         }
 
+
         /**
          * Show some instructions to the user only if they are using keyboard navigation - for example, a prompt on how to navigate with the keyboard if Tab is repurposed.
          * @param {string} instructions The instructions to display only if keyboard navigation is being used. If it's blank, no instructions will be shown.
@@ -739,7 +804,6 @@ var codeInput = {
             this.codeElement = code;
             pre.append(code);
             this.append(pre);
-
             if (this.templateObject.isCode) {
                 if (lang != undefined && lang != "") {
                     code.classList.add("language-" + lang.toLowerCase());
@@ -765,7 +829,6 @@ var codeInput = {
             // Update with fallback textarea's state so can keep editing
             // if loaded slowly
             if(fallbackSelectionStart !== undefined) {
-                console.log("sel", fallbackSelectionStart, fallbackSelectionEnd, fallbackSelectionDirection, "scr", fallbackScrollTop, fallbackScrollLeft, "foc", fallbackFocused);
                 textarea.setSelectionRange(fallbackSelectionStart, fallbackSelectionEnd, fallbackSelectionDirection);
                 textarea.scrollTo(fallbackScrollTop, fallbackScrollLeft);
             }
@@ -779,7 +842,44 @@ var codeInput = {
                 // The only element that could be resized is this code-input element.
                 this.syncSize();
             });
-            resizeObserver.observe(this.textareaElement);
+            resizeObserver.observe(this);
+
+
+            // Add internal style as non-externally-overridable alternative to style attribute for e.g. syncing color
+            this.classList.add("code-input_styles_" + codeInput.stylesheetI);
+            const stylesheet = document.createElement("style");
+            stylesheet.innerHTML = "code-input.code-input_styles_" + codeInput.stylesheetI + " {}";
+            this.appendChild(stylesheet);
+            this.internalStyle = stylesheet.sheet.cssRules[0].style;
+            codeInput.stylesheetI++;
+
+            // Synchronise colors
+            const preColorChangeCallback = (evt) => {
+                if(evt.propertyName == "color") {
+                    this.isColorOverridenSyncIfNot();
+                }
+            };
+            this.preElement.addEventListener("transitionend", preColorChangeCallback);
+            this.preElement.addEventListener("-webkit-transitionend", preColorChangeCallback);
+            const thisColorChangeCallback = (evt) => {
+                if(evt.propertyName == "color") {
+                    this.syncColorCompletely();
+                }
+                if(evt.target == this.dialogContainerElement) {
+                    evt.stopPropagation();
+                    // Prevent bubbling because code-input
+                    // transitionend is separate
+                }
+            };
+            // Not on this element so CSS transition property does not override publicly-visible one
+            this.dialogContainerElement.addEventListener("transitionend", thisColorChangeCallback);
+            this.dialogContainerElement.addEventListener("-webkit-transitionend", thisColorChangeCallback);
+
+            // For when this code-input element has an externally-defined, different-duration transition
+            this.addEventListener("transitionend", thisColorChangeCallback);
+            this.addEventListener("-webkit-transitionend", thisColorChangeCallback);
+
+            this.syncColorCompletely();
 
             this.classList.add("code-input_loaded");
         }
@@ -914,7 +1014,9 @@ var codeInput = {
                             code.classList.add("language-" + newValue);
                         }
 
-                        if (mainTextarea.placeholder == oldValue) mainTextarea.placeholder = newValue;
+                        if (mainTextarea.placeholder == oldValue || oldValue == null && mainTextarea.placeholder == "") {
+                            mainTextarea.placeholder = newValue;
+                        }
 
                         this.scheduleHighlight();
 

docs/interface/css/_index.md

@@ -10,3 +10,6 @@ title = 'Styling `code-input` elements with CSS'
 * The CSS variable `--padding` should be used rather than the property `padding` (e.g. `<code-input style="--padding: 10px;">...`), or `--padding-left`, `--padding-right`, `--padding-top` and `--padding-bottom` instead of the CSS properties of the same names. For technical reasons, the value must have a unit (i.e. `0px`, not `0`).
 * Background colours set on `code-input` elements will not work with highlighters that set background colours themselves - use `(code-input's selector) pre[class*="language-"]` for Prism.js or `.hljs` for highlight.js to target the highlighted element with higher specificity than the highlighter's theme. You may also set the `background-color` of the code-input element for its appearance when its template is unregistered / there is no JavaScript.
 * For now, elements on top of `code-input` elements should have a CSS `z-index` at least 3 greater than the `code-input` element.
+* The caret and placeholder colour by default follow and give good contrast with the highlighted theme. Setting a CSS rule (with a specificity higher than one element and one class, for good backwards compatibility) for `color` and/or `caret-color` properties on the code-input element will override this behaviour.
+
+Please do **not** use `className` in JavaScript referring to code-input elements, because the code-input library needs to add its own classes to code-input elements for easier progressive enhancement. You can, however, use `classList` and `style` as much as you want - it will make your code cleaner anyway.

tests/hljs.html

@@ -6,7 +6,7 @@
     <title>code-input Tester</title>
 
     <!--Import Highlight.JS-->
-    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.9.0/styles/default.min.css">
+    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.9.0/styles/default.min.css" id="theme-stylesheet">
     <script src="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.9.0/highlight.min.js"></script>
     <script src="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.9.0/languages/xml.min.js"></script>
     <script src="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.9.0/languages/css.min.js"></script>
@@ -42,7 +42,7 @@ <h4><a href="prism.html">Test for Prism.js</a></h4>
 
     <details id="collapse-results"><summary>Test Results (Click to Open)</summary><pre id="test-results"></pre></details>
     <form method="GET" action="afterform.html" target="_blank">
-        <code-input><textarea data-code-input-fallback name="q">console.log("Hello, World!");
+        <code-input><textarea data-code-input-fallback name="q" placeholder="language auto-detected">console.log("Hello, World!");
 // A second line
 // A third line with &lt;html> tags</textarea></code-input>
         <input type="submit" value="Test HTML Form"/>

tests/prism.html

@@ -5,7 +5,7 @@
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <title>code-input Tester</title>
     <!--Import Prism-->
-    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/prism/1.29.0/themes/prism.min.css">
+    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/prism/1.29.0/themes/prism.min.css" id="theme-stylesheet">
     <script src="https://cdnjs.cloudflare.com/ajax/libs/prism/1.29.0/prism.min.js" data-manual></script><!--Remove data-manual if also using Prism normally-->
     <script src="https://cdnjs.cloudflare.com/ajax/libs/prism/1.29.0/plugins/autoloader/prism-autoloader.min.js"></script>
     <script src="https://cdnjs.cloudflare.com/ajax/libs/prism/1.29.0/plugins/line-numbers/prism-line-numbers.min.js"></script>

tests/tester.js

@@ -326,6 +326,34 @@ console.log("I've got another line!", 2 < 3, "should be true.");
 // A third line with <html> tags
 `); // Extra newline so line numbers visible if enabled.
 
+    // Delete all code
+    textarea.selectionStart = 0;
+    textarea.selectionEnd = textarea.value.length;
+    backspace(textarea);
+    codeInputElement.setAttribute("language", "JavaScript"); // for placeholder
+
+    await waitAsync(100); // Wait for rendered value to update
+    testAssertion("Core", "Light theme Caret/Placeholder Color Correct", confirm("Are the caret and placeholder near-black? (OK=Yes)"), "user-judged");
+
+    if(isHLJS) {
+        document.getElementById("theme-stylesheet").href = "https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.9.0/styles/dark.min.css";
+    } else {
+        document.getElementById("theme-stylesheet").href = "https://cdnjs.cloudflare.com/ajax/libs/prism/1.29.0/themes/prism-okaidia.min.css";
+    }
+    await waitAsync(200); // Wait for colours to update
+    testAssertion("Core", "Dark theme Caret/Placeholder Color Correct", confirm("Are the caret and placeholder near-white? (OK=Yes)"), "user-judged");
+
+    codeInputElement.style.color = "red";
+    await waitAsync(200); // Wait for colours to update
+    testAssertion("Core", "Overriden color Caret/Placeholder Color Correct", confirm("Are the caret and placeholder (for Firefox) or just caret (for Chromium/WebKit, for consistency with textareas) red? (OK=Yes)"), "user-judged");
+
+    codeInputElement.style.removeProperty("color");
+    codeInputElement.style.caretColor = "red";
+    await waitAsync(200); // Wait for colours to update
+    testAssertion("Core", "Overriden caret-color Caret/Placeholder Color Correct", confirm("Is the caret red and placeholder near-white? (OK=Yes)"), "user-judged");
+
+    codeInputElement.style.removeProperty("caret-color");
+
     /*--- Tests for plugins ---*/
     // AutoCloseBrackets
     testAddingText("AutoCloseBrackets", textarea, function(textarea) {