Not supported property values

editor/css/editable-css.css

@@ -126,7 +126,7 @@
 }
 
 @media screen and (min-width: 590px) {
-  .example-choice.selected:before {
+  .example-choice.selected:before, .example-choice.invalid:before {
     opacity: 1;
     right: -1rem;
   }

editor/js/editable-css.js

@@ -1,6 +1,7 @@
 import * as clippy from "./editor-libs/clippy.js";
 import * as mceEvents from "./editor-libs/events.js";
 import * as mceUtils from "./editor-libs/mce-utils.js";
+import * as cssEditorUtils from "./editor-libs/css-editor-utils.js";
 
 import "../css/editor-libs/ui-fonts.css";
 import "../css/editor-libs/common.css";
@@ -47,6 +48,8 @@ import "../css/editable-css.css";
     mceEvents.register();
     handleResetEvents();
     handleChoiceHover();
+    // Adding or removing class "invalid"
+    cssEditorUtils.applyInitialSupportWarningState(exampleChoices);
 
     clippy.addClippy();
   }
@@ -70,6 +73,9 @@ import "../css/editable-css.css";
         exampleChoices[i].querySelector("code").innerHTML = highlighted;
       }
 
+      // Adding or removing class "invalid"
+      cssEditorUtils.applyInitialSupportWarningState(exampleChoices);
+
       // if there is an initial choice set, set it as selected
       if (initialChoice) {
         mceEvents.onChoose(exampleChoices[initialChoice]);

editor/js/editor-libs/css-editor-utils.js

@@ -1,27 +1,129 @@
 export let editTimer = undefined;
 
-export function applyCode(code, choice, targetElement) {
+export function applyCode(code, choice, targetElement, immediateInvalidChange) {
   // http://regexr.com/3fvik
   var cssCommentsMatch = /(\/\*)[\s\S]+(\*\/)/g;
   var element = targetElement || document.getElementById("example-element");
 
   // strip out any CSS comments before applying the code
-  code.replace(cssCommentsMatch, "");
+  code = code.replace(cssCommentsMatch, "");
+    // Checking if every CSS declaration in passed code, is supported by the browser
+    let codeSupported = isCodeSupported(element, code);
 
   element.style.cssText = code;
 
   // clear any existing timer
   clearTimeout(editTimer);
-  /* Start a new timer. This will ensure that the state is
-        not marked as invalid, until the user has stopped typing
-        for 500ms */
-  editTimer = setTimeout(function () {
-    if (!element.style.cssText) {
-      choice.parentNode.classList.add("invalid");
+
+  /**
+   * Adding or removing class "invalid" from choice parent, which will typically be <div class="example-choice">
+   */
+  let setInvalidClass = function() {
+    if (codeSupported) {
+      choice.parentNode.classList.remove('invalid');
     } else {
-      choice.parentNode.classList.remove("invalid");
+      choice.parentNode.classList.add('invalid');
+    }
+  };
+
+  if(immediateInvalidChange) {
+    // Setting class immediately
+    setInvalidClass();
+  } else {
+    /* Start a new timer. This will ensure that the state is
+    not marked as invalid, until the user has stopped typing
+    for 500ms */
+    editTimer = setTimeout(setInvalidClass, 500);
+  }
+}
+
+/**
+ * Checks if every passed declaration is supported by the browser.
+ * In case browser recognizes property with vendor prefix(like -webkit-), lacking support for unprefixed property is ignored.
+ * Properties with vendor prefix not recognized by the browser are always ignored.
+ * @param element - any element on which cssText can be tested
+ * @param declarations - list of css declarations with no curly brackets. They need to be separated by ";" and declaration key-value needs to be separated by ":". Function expects no comments.
+ * @returns {boolean} - true if every declaration is supported by the browser. Properties with vendor prefix are excluded.
+ */
+export function isCodeSupported(element, declarations) {
+    var vendorPrefixMatch = /^-(?:webkit|moz|ms|o)-/;
+    var style = element.style;
+    // Expecting declarations to be separated by ";"
+    // Declarations with just white space are ignored
+    var declarationsArray = declarations.split(";")
+        .map(d => d.trim())
+        .filter(d => d.length > 0);
+
+    /**
+     * @returns {boolean} - true if declaration starts with -webkit-, -moz-, -ms- or -o-
+     */
+    function hasVendorPrefix(declaration) {
+        return vendorPrefixMatch.test(declaration);
+    }
+
+    /**
+     * Looks for property name by cutting off optional vendor prefix at the beginning
+     * and then cutting off rest of the declaration, starting from any whitespace or ":" in property name.
+     * @param declaration - single css declaration, with not white space at the beginning
+     * @returns {string} - property name without vendor prefix.
+     */
+    function getPropertyNameNoPrefix(declaration) {
+        var prefixMatch = vendorPrefixMatch.exec(declaration);
+        var prefix = prefixMatch === null ? "" : prefixMatch[0];
+        var declarationNoPrefix = prefix === null ? declaration : declaration.slice(prefix.length);
+        // Expecting property name to be over, when any whitespace or ":" is found
+        var propertyNameSeparator = /[\s:]/;
+        return declarationNoPrefix.split(propertyNameSeparator)[0];
+    }
+    // Clearing previous state
+    style.cssText = "";
+
+    // List of found and applied properties with vendor prefix
+    let appliedPropertiesWithPrefix = new Set();
+    // List of not applied properties - because of lack of support for its name or value
+    let notAppliedProperties = new Set();
+
+    for (let declaration of declarationsArray) {
+        let previousCSSText = style.cssText;
+        // Declarations are added one by one, because browsers sometimes combine multiple declarations into one
+        // For example Chrome changes "column-count: auto;column-width: 8rem;" into "columns: 8rem auto;"
+        style.cssText += declaration + ";"; // ";" was previous removed while using split method
+        // In case property name or value is not supported, browsers skip single declaration, while leaving rest of them intact
+        let correctlyApplied = style.cssText !== previousCSSText;
+
+        let vendorPrefixFound = hasVendorPrefix(declaration);
+        let propertyName = getPropertyNameNoPrefix(declaration);
+
+        if (correctlyApplied && vendorPrefixFound) {
+            // We are saving applied properties with prefix, so equivalent property with no prefix doesn't need to be supported
+            appliedPropertiesWithPrefix.add(propertyName);
+        } else if (!correctlyApplied && !vendorPrefixFound) {
+            notAppliedProperties.add(propertyName);
+        }
+    }
+
+    if (notAppliedProperties.size !== 0) {
+        // If property with vendor prefix is supported, we can ignore the fact that browser doesn't support property with no prefix
+        for (let substitute of appliedPropertiesWithPrefix) {
+            notAppliedProperties.delete(substitute);
+        }
+        // If any other declaration is not supported, whole block should be marked as invalid
+        if (notAppliedProperties.size !== 0)
+            return false;
+    }
+    return true;
+}
+
+/**
+ * Checking support for choices inner code and based on that information adding or removing class "invalid" from them.
+ * This function will change styles of 'example-element', so it is important to apply them again.
+ * @param choices - elements containing element code, containing css declarations to apply
+ */
+export function applyInitialSupportWarningState(choices) {
+    for(let choice of choices) {
+        let codeBlock = choice.querySelector("code");
+        applyCode(codeBlock.textContent, codeBlock.parentNode, undefined, true);
     }
-  }, 500);
 }
 
 /**
@@ -38,7 +140,7 @@ export function choose(choice) {
   codeBlock.setAttribute("contentEditable", true);
   codeBlock.setAttribute("spellcheck", false);
 
-  applyCode(codeBlock.textContent, choice);
+  applyCode(codeBlock.textContent, codeBlock.parentNode);
 }
 
 /**
@@ -65,7 +167,7 @@ export function resetDefault() {
 }
 
 /**
- * Resets the UI state by deselcting all example choice
+ * Resets the UI state by deselecting all example choice
  */
 export function resetUIState() {
   var exampleChoiceList = document.getElementById("example-choice-list");