js: Implement DynamicText class.

This implements the DynamicText class for resizing of text to fit the
parent node.

.eslintrc.json

@@ -16,6 +16,7 @@
         "marked": false,
         "moment": false,
         "i18n": false,
+        "DynamicText": false,
         "bridge": false,
         "page_params": false,
         "status_classes": false,

static/js/dynamic_text.js

@@ -0,0 +1,97 @@
+// This is a public instance of the `DynamicText` class.
+// The `DynamicText` object serves to resize text that is set through its
+// public methods so that the text won't ever overrun the parent container.
+var DynamicText = (function () {
+    // the initialization of the `DynamicText` instance.
+    var DynamicText = function ($parent) {
+        if (typeof jQuery !== "undefined" && $parent instanceof jQuery) {
+            // we grab the first element in a jQuery list to run DynamicText on.
+            this.parent = $parent[0];
+        } else if ($parent instanceof Node) {
+            // this is a node rather than a list, so we just take the element given
+            // to run DynamicText on.
+            this.parent = $parent;
+        }
+
+        this.node = document.createElement("span");
+        this.node.style.whiteSpace = "nowrap";
+
+        this.prev_content = this.parent.innerHTML;
+        this.parent.innerHTML = "";
+        this.parent.appendChild(this.node);
+
+        this.update();
+    };
+
+    // an object for private functions that are inaccessible to the outside
+    // world.
+    var internal_funcs = {
+        insertText: function (type, text, node, parent) {
+            if (type === DynamicText.prototype.TYPE.TEXT) {
+                node.innerText = text;
+            } else if (type === DynamicText.prototype.TYPE.HTML) {
+                node.innerHTML = text;
+            } else {
+                blueslip.error("The method '" + type + "' is not a valid " +
+                              " DynamicText input method.");
+            }
+
+            // reset the font-size to inherit the parent's size; 1em.
+            node.style.fontSize = "1em";
+
+            var width = {
+                node: node.offsetWidth,
+                parent: parent.clientWidth,
+            };
+
+            // if the width is larger than the parent, resize by the ratio of
+            // the parent's width to the node's width.
+            if (width.node > width.parent) {
+                node.style.fontSize = (width.parent / width.node) + "em";
+            } else {
+                node.style.fontSize = "1em";
+            }
+        },
+    };
+
+    DynamicText.prototype = {
+        // insertion enum types.
+        TYPE: {
+            TEXT: 1,
+            HTML: 2,
+        },
+
+        // re-set the content inside the span element and process for width.
+        // the structure goes like:
+        // FROM:    <parent>content</parent>
+        // TO:      <parent>
+        //              <span style="font-size: {{ value }}">content</span>
+        //          </parent>
+        update: function () {
+            // call `text` by default since if HTML is needed (unsafe), it can be
+            // done manually.
+            this.text(this.prev_content);
+        },
+
+        // this takes about 0.005ms for items that don't need resizing and 0.08ms
+        // for items that do need resizing.
+        text: function (text) {
+            internal_funcs.insertText(this.TYPE.TEXT, text, this.node, this.parent);
+        },
+
+        // this function takes approx 0.4ms/iteration.
+        // the speed is mostly limited to the slowness of the innerHTML function.
+        html: function (html) {
+            internal_funcs.insertText(this.TYPE.HTML, html, this.node, this.parent);
+        },
+    };
+
+    // keep these arguments updated with `DynamicText` class constructor.
+    return function ($node) {
+        return new DynamicText($node);
+    };
+}());
+
+if (typeof module !== 'undefined') {
+    module.exports = DynamicText;
+}

zproject/settings.py

@@ -854,6 +854,7 @@ JS_SPECS = {
             'js/feature_flags.js',
             'js/loading.js',
             'js/util.js',
+            'js/dynamic_text.js',
             'js/rtl.js',
             'js/dict.js',
             'js/components.js',