Turns out this is really not an easy thing to do. I've been struggling with it for the past few days, and I'm not very close to a solution.
Your best drop-in solution currently is the At.js library, which is still being maintained, but definitely isn't perfect. One of the examples shows how you can kind of do a text highlight.
The most annoying part of this problem is that Twitter has a beautiful solution that seemingly works perfectly staring us right in the face. I took some time investigating the way they implement their "tweet box," and it's definitely not trivial. It looks like they're doing almost everything manually, including emulating undo/redo functionality, intercepting copy/pastes, providing custom code for IE/W3C, custom-coding Mac/PC, and more. They use a contenteditable div, which is in-and-of-itself problematic due to differences in browser implementations. It's pretty impressive, actually.
Here's the most relevant (obfuscated, unfortunately) code, taken from Twitter's boot JavaScript file (found by inspecting the header of the logged-in Twitter homepage). I didn't want to directly copy and paste the link, in case it's personalized to my Twitter account.
define("app/utils/html_text", ["module", "require", "exports"], function(module, require, exports) {
function isTextNode(a) {
return a.nodeType == 3 || a.nodeType == 4
}
function isElementNode(a) {
return a.nodeType == 1
}
function isBrNode(a) {
return isElementNode(a) && a.nodeName.toLowerCase() == "br"
}
function isOutsideContainer(a, b) {
while (a !== b) {
if (!a) return !0;
a = a.parentNode
}
}
var useW3CRange = window.getSelection,
useMsftTextRange = !useW3CRange && document.selection,
useIeHtmlFix = navigator.appName == "Microsoft Internet Explorer",
NBSP_REGEX = /[\xa0\n\t]/g,
CRLF_REGEX = /\r\n/g,
LINES_REGEX = /(.*?)\n/g,
SP_LEADING_OR_FOLLOWING_CLOSE_TAG_OR_PRECEDING_A_SP_REGEX = /^ |(<\/[^>]+>) | (?= )/g,
SP_LEADING_OR_TRAILING_OR_FOLLOWING_A_SP_REGEX = /^ | $|( ) /g,
MAX_OFFSET = Number.MAX_VALUE,
htmlText = function(a, b) {
function c(a, c) {
function h(a) {
var i = d.length;
if (isTextNode(a)) {
var j = a.nodeValue.replace(NBSP_REGEX, " "),
k = j.length;
k && (d += j, e = !0), c(a, !0, 0, i, i + k)
} else if (isElementNode(a)) {
c(a, !1, 0, i, i);
if (isBrNode(a)) a == f ? g = !0 : (d += "\n", e = !1);
else {
var l = a.currentStyle || window.getComputedStyle(a, ""),
m = l.display == "block";
m && b.msie && (e = !0);
for (var n = a.firstChild, o = 1; n; n = n.nextSibling, o++) {
h(n);
if (g) return;
i = d.length, c(a, !1, o, i, i)
}
g || a == f ? g = !0 : m && e && (d += "\n", e = !1)
}
}
}
var d = "",
e, f, g;
for (var i = a; i && isElementNode(i); i = i.lastChild) f = i;
return h(a), d
}
function d(a, b) {
var d = null,
e = b.length - 1;
if (useW3CRange) {
var f = b.map(function() {
return {}
}),
g;
c(a, function(a, c, d, h, i) {
g || f.forEach(function(f, j) {
var k = b[j];
h <= k && !isBrNode(a) && (f.node = a, f.offset = c ? Math.min(k, i) - h : d, g = c && j == e && i >= k)
})
}), f[0].node && f[e].node && (d = document.createRange(), d.setStart(f[0].node, f[0].offset), d.setEnd(f[e].node, f[e].offset))
} else if (useMsftTextRange) {
var h = document.body.createTextRange();
h.moveToElementText(a), d = h.duplicate();
if (b[0] == MAX_OFFSET) d.setEndPoint("StartToEnd", h);
else {
d.move("character", b[0]);
var i = e && b[1] - b[0];
i > 0 && d.moveEnd("character", i), h.inRange(d) || d.setEndPoint("EndToEnd", h)
}
}
return d
}
function e() {
return document.body.contains(a)
}
function f(b) {
a.innerHTML = b;
if (useIeHtmlFix)
for (var c = a.firstChild; c; c = c.nextSibling) isElementNode(c) && c.nodeName.toLowerCase() == "p" && c.innerHTML == "" && (c.innerText = "")
}
function g(a, b) {
return a.map(function(a) {
return Math.min(a, b.length)
})
}
function h() {
var b = getSelection();
if (b.rangeCount !== 1) return null;
var d = b.getRangeAt(0);
if (isOutsideContainer(d.commonAncestorContainer, a)) return null;
var e = [{
node: d.startContainer,
offset: d.startOffset
}];
d.collapsed || e.push({
node: d.endContainer,
offset: d.endOffset
});
var f = e.map(function() {
return MAX_OFFSET
}),
h = c(a, function(a, b, c, d) {
e.forEach(function(e, g) {
f[g] == MAX_OFFSET && a == e.node && (b || c == e.offset) && (f[g] = d + (b ? e.offset : 0))
})
});
return g(f, h)
}
function i() {
var b = document.selection.createRange();
if (isOutsideContainer(b.parentElement(), a)) return null;
var d = ["Start"];
b.compareEndPoints("StartToEnd", b) && d.push("End");
var e = d.map(function() {
return MAX_OFFSET
}),
f = document.body.createTextRange(),
h = c(a, function(c, g, h, i) {
function j(a, c) {
if (e[c] < MAX_OFFSET) return;
var d = f.compareEndPoints("StartTo" + a, b);
if (d > 0) return;
var g = f.compareEndPoints("EndTo" + a, b);
if (g < 0) return;
var h = f.duplicate();
h.setEndPoint("EndTo" + a, b), e[c] = i + h.text.length, c && !g && e[c]++
}!g && !h && c != a && (f.moveToElementText(c), d.forEach(j))
});
return g(e, h)
}
return {
getHtml: function() {
if (useIeHtmlFix) {
var b = "",
c = document.createElement("div");
for (var d = a.firstChild; d; d = d.nextSibling) isTextNode(d) ? (c.innerText = d.nodeValue, b += c.innerHTML) : b += d.outerHTML.replace(CRLF_REGEX, "");
return b
}
return a.innerHTML
},
setHtml: function(a) {
f(a)
},
getText: function() {
return c(a, function() {})
},
setTextWithMarkup: function(a) {
f((a + "\n").replace(LINES_REGEX, function(a, c) {
return b.mozilla || b.msie ? (c = c.replace(SP_LEADING_OR_FOLLOWING_CLOSE_TAG_OR_PRECEDING_A_SP_REGEX, "$1 "), b.mozilla ? c + "<BR>" : "<P>" + c + "</P>") : (c = (c || "<br>").replace(SP_LEADING_OR_TRAILING_OR_FOLLOWING_A_SP_REGEX, "$1 "), b.opera ? "<p>" + c + "</p>" : "<div>" + c + "</div>")
}))
},
getSelectionOffsets: function() {
var a = null;
return e() && (useW3CRange ? a = h() : useMsftTextRange && (a = i())), a
},
setSelectionOffsets: function(b) {
if (b && e()) {
var c = d(a, b);
if (c)
if (useW3CRange) {
var f = window.getSelection();
f.removeAllRanges(), f.addRange(c)
} else useMsftTextRange && c.select()
}
},
emphasizeText: function(b) {
var f = [];
b && b.length > 1 && e() && (c(a, function(a, c, d, e, g) {
if (c) {
var h = Math.max(e, b[0]),
i = Math.min(g, b[1]);
i > h && f.push([h, i])
}
}), f.forEach(function(b) {
var c = d(a, b);
c && (useW3CRange ? c.surroundContents(document.createElement("em")) : useMsftTextRange && c.execCommand("italic", !1, null))
}))
}
}
};
module.exports = htmlText
});
define("app/utils/tweet_helper", ["module", "require", "exports", "lib/twitter-text", "core/utils", "app/data/user_info"], function(module, require, exports) {
var twitterText = require("lib/twitter-text"),
utils = require("core/utils"),
userInfo = require("app/data/user_info"),
VALID_PROTOCOL_PREFIX_REGEX = /^https?:\/\//i,
tweetHelper = {
extractMentionsForReply: function(a, b) {
var c = a.attr("data-screen-name"),
d = a.attr("data-retweeter"),
e = a.attr("data-mentions") ? a.attr("data-mentions").split(" ") : [],
f = a.attr("data-tagged") ? a.attr("data-tagged").split(" ") : [];
e = e.concat(f);
var g = [c, b, d];
return e = e.filter(function(a) {
return g.indexOf(a) < 0
}), d && d != c && d != b && e.unshift(d), (!e.length || c != b) && e.unshift(c), e
},
linkify: function(a, b) {
return b = utils.merge({
hashtagClass: "twitter-hashtag pretty-link",
hashtagUrlBase: "/search?q=%23",
symbolTag: "s",
textWithSymbolTag: "b",
cashtagClass: "twitter-cashtag pretty-link",
cashtagUrlBase: "/search?q=%24",
usernameClass: "twitter-atreply pretty-link",
usernameUrlBase: "/",
usernameIncludeSymbol: !0,
listClass: "twitter-listname pretty-link",
urlClass: "twitter-timeline-link",
urlTarget: "_blank",
suppressNoFollow: !0,
htmlEscapeNonEntities: !0
}, b || {}), twitterText.autoLinkEntities(a, twitterText.extractEntitiesWithIndices(a), b)
}
};
module.exports = tweetHelper
});
define("app/ui/compose/with_rich_editor", ["module", "require", "exports", "app/utils/file", "app/utils/html_text", "app/utils/tweet_helper", "lib/twitter-text"], function(module, require, exports) {
function withRichEditor() {
this.defaultAttrs({
richSelector: "div.rich-editor",
linksSelector: "a",
normalizerSelector: "div.rich-normalizer",
$browser: $.browser
}), this.linkify = function(a) {
var b = {
urlTarget: null,
textWithSymbolTag: RENDER_URLS_AS_PRETTY_LINKS ? "b" : "",
linkAttributeBlock: function(a, b) {
var c = a.screenName || a.url;
c && (this.urlAndMentionsCharCount += c.length + 2), delete b.title, delete b["data-screen-name"], b.dir = a.hashtag && this.shouldBeRTL(a.hashtag, 0) ? "rtl" : "ltr", b.role = "presentation"
}.bind(this)
};
return this.urlAndMentionsCharCount = 0, tweetHelper.linkify(a, b)
}, this.around("setSelection", function(a, b) {
b && this.setSelectionIfFocused(b)
}), this.around("setCursorPosition", function(a, b) {
b === undefined && (b = this.attr.cursorPosition), b === undefined && (b = MAX_OFFSET), this.setSelectionIfFocused([b])
}), this.around("detectUpdatedText", function(a, b, c) {
var d = this.htmlRich.getHtml(),
e = this.htmlRich.getSelectionOffsets() || [MAX_OFFSET],
f = c !== undefined;
if (d === this.prevHtml && e[0] === this.prevSelectionOffset && !b && !f) return;
var g = f ? c : this.htmlRich.getText(),
h = g.replace(INVALID_CHARS_REGEX, "");
(f || !(!d && !this.hasFocus() || this.$text.attr("data-in-composition"))) && this.reformatHtml(h, d, e, f);
if (b || this.cleanedText != h || this.prevSelectionOffset != e[0]) this.prevSelectionOffset = e[0], this.updateCleanedTextAndOffset(h, e[0])
}), this.reformatHtml = function(a, b, c, d) {
this.htmlNormalizer.setTextWithMarkup(this.linkify(a)), this.interceptDataImageInContent();
var e = this.shouldBeRTL(a, this.urlAndMentionsCharCount);
this.$text.attr("dir", e ? "rtl" : "ltr"), this.$normalizer.find(e ? "[dir=rtl]" : "[dir=ltr]").removeAttr("dir"), RENDER_URLS_AS_PRETTY_LINKS && this.$normalizer.find(".twitter-timeline-link").wrapInner("<b>").addClass("pretty-link");
var f = this.getMaxLengthOffset(a);
f >= 0 && (this.htmlNormalizer.emphasizeText([f, MAX_OFFSET]), this.$normalizer.find("em").each(function() {
this.innerHTML = this.innerHTML.replace(TRAILING_SINGLE_SPACE_REGEX, "Â ")
}));
var g = this.htmlNormalizer.getHtml();
if (g !== b) {
var h = d && !this.isFocusing && this.hasFocus();
h && this.$text.addClass("fake-focus").blur(), this.htmlRich.setHtml(g), h && this.$text.focus().removeClass("fake-focus"), this.setSelectionIfFocused(c)
}
this.prevHtml = g
}, this.interceptDataImageInContent = function() {
if (!this.triggerGotImageData) return;
this.$text.find("img").filter(function(a, b) {
return b.src.match(/^data:/)
}).first().each(function(a, b) {
var c = file.getBlobFromDataUri(b.src);
file.getFileData("pasted.png", c).then(this.triggerGotImageData.bind(this))
}.bind(this))
}, this.getMaxLengthOffset = function(a) {
var b = this.getLength(a),
c = this.attr.maxLength;
if (b <= c) return -1;
c += twitterText.getUnicodeTextLength(a) - b;
var d = [{
indices: [c, c]
}];
return twitterText.modifyIndicesFromUnicodeToUTF16(a, d), d[0].indices[0]
}, this.setSelectionIfFocused = function(a) {
this.hasFocus() ? (this.previousSelection = null, this.htmlRich.setSelectionOffsets(a)) : this.previousSelection = a
}, this.selectPrevCharOnBackspace = function(a) {
if (a.which == 8 && !a.ctrlKey) {
var b = this.htmlRich.getSelectionOffsets();
b && b[0] != MAX_OFFSET && b.length == 1 && (b[0] ? this.setSelectionIfFocused([b[0] - 1, b[0]]) : this.stopEvent(a))
}
}, this.emulateCommandArrow = function(a) {
if (a.metaKey && !a.shiftKey && (a.which == 37 || a.which == 39)) {
var b = a.which == 37;
this.htmlRich.setSelectionOffsets([b ? 0 : MAX_OFFSET]), this.$text.scrollTop(b ? 0 : this.$text[0].scrollHeight), this.stopEvent(a)
}
}, this.stopEvent = function(a) {
a.preventDefault(), a.stopPropagation()
}, this.saveUndoStateDeferred = function(a) {
if (a.type == "mousemove" && a.which != 1) return;
setTimeout(function() {
this.detectUpdatedText(), this.saveUndoState()
}.bind(this), 0)
}, this.clearUndoState = function() {
this.undoHistory = [], this.undoIndex = -1
}, this.saveUndoState = function() {
var a = this.htmlRich.getText(),
b = this.htmlRich.getSelectionOffsets() || [a.length],
c = this.undoHistory,
d = c[this.undoIndex];
!d || d[0] !== a ? c.splice(++this.undoIndex, c.length, [a, b]) : d && (d[1] = b)
}, this.isUndoKey = function(a) {
return this.isMac ? a.which == 90 && a.metaKey && !a.shiftKey && !a.ctrlKey && !a.altKey : a.which == 90 && a.ctrlKey && !a.shiftKey && !a.altKey
}, this.emulateUndo = function(a) {
this.isUndoKey(a) && (this.stopEvent(a), this.saveUndoState(), this.undoIndex > 0 && this.setUndoState(this.undoHistory[--this.undoIndex]))
}, this.isRedoKey = function(a) {
return this.isMac ? a.which == 90 && a.metaKey && a.shiftKey && !a.ctrlKey && !a.altKey : this.isWin ? a.which == 89 && a.ctrlKey && !a.shiftKey && !a.altKey : a.which == 90 && a.shiftKey && a.ctrlKey && !a.altKey
}, this.emulateRedo = function(a) {
var b = this.undoHistory,
c = this.undoIndex;
c < b.length - 1 && this.htmlRich.getText() !== b[c][0] && b.splice(c + 1, b.length), this.isRedoKey(a) && (this.stopEvent(a), c < b.length - 1 && this.setUndoState(b[++this.undoIndex]))
}, this.setUndoState = function(a) {
this.detectUpdatedText(!1, a[0]), this.htmlRich.setSelectionOffsets(a[1]), this.trigger("uiHideAutocomplete")
}, this.undoStateAfterCursorMovement = function(a) {
a.which >= 33 && a.which <= 40 && this.saveUndoStateDeferred(a)
}, this.handleKeyDown = function(a) {
this.isIE && this.selectPrevCharOnBackspace(a), this.attr.$browser.mozilla && this.emulateCommandArrow(a), this.undoStateAfterCursorMovement(a), this.emulateUndo(a), this.emulateRedo(a)
}, this.interceptPaste = function(a) {
if (a.originalEvent && a.originalEvent.clipboardData) {
var b = a.originalEvent.clipboardData;
(this.interceptImagePaste(b) || this.interceptTextPaste(b)) && a.preventDefault()
}
}, this.interceptImagePaste = function(a) {
return this.triggerGotImageData && a.items && a.items.length === 1 && a.items[0].kind === "file" && a.items[0].type.indexOf("image/") === 0 ? (file.getFileData("pasted.png", a.items[0].getAsFile()).then(this.triggerGotImageData.bind(this)), !0) : !1
}, this.interceptTextPaste = function(a) {
var b = a.getData("text");
return b && document.execCommand("insertHTML", !1, $("<div>").text(b).html().replace(LINE_FEEDS_REGEX, "<br>")) ? !0 : !1
}, this.clearSelectionOnBlur = function() {
window.getSelection && (this.previousSelection = this.htmlRich.getSelectionOffsets(), this.previousSelection && getSelection().removeAllRanges())
}, this.restoreSelectionOnFocus = function() {
this.previousSelection ? setTimeout(function() {
this.htmlRich.setSelectionOffsets(this.previousSelection), this.previousSelection = null
}.bind(this), 0) : this.previousSelection = null
}, this.setFocusingState = function() {
this.isFocusing = !0, setTimeout(function() {
this.isFocusing = !1
}.bind(this), 0)
}, this.around("initTextNode", function(a) {
this.isIE = this.attr.$browser.msie || navigator.userAgent.indexOf("Trident") > -1, this.$text = this.select("richSelector"), this.undoHistory = [
["", [0]]
], this.undoIndex = 0, this.htmlRich = htmlText(this.$text[0], this.attr.$browser), this.$text.toggleClass("notie", !this.isIE), this.$normalizer = this.select("normalizerSelector"), this.htmlNormalizer = htmlText(this.$normalizer[0], this.attr.$browser);
var b = navigator.platform;
this.isMac = b.indexOf("Mac") != -1, this.isWin = b.indexOf("Win") != -1, this.on(this.$text, "click", {
linksSelector: this.stopEvent
}), this.on(this.$text, "focusin", this.setFocusingState), this.on(this.$text, "keydown", this.handleKeyDown), this.on(this.$text, "focusout", this.ignoreDuringFakeFocus(this.clearSelectionOnBlur)), this.on(this.$text, "focusin", this.ignoreDuringFakeFocus(this.restoreSelectionOnFocus)), this.on(this.$text, "focusin", this.ignoreDuringFakeFocus(this.saveUndoStateDeferred)), this.on(this.$text, "cut paste drop", this.saveUndoState), this.on(this.$text, "cut paste drop mousedown mousemove", this.saveUndoStateDeferred), this.on("uiSaveUndoState", this.saveUndoState), this.on("uiClearUndoState", this.clearUndoState), this.on(this.$text, "paste", this.interceptPaste), this.detectUpdatedText()
})
}
var file = require("app/utils/file"),
htmlText = require("app/utils/html_text"),
tweetHelper = require("app/utils/tweet_helper"),
twitterText = require("lib/twitter-text");
module.exports = withRichEditor;
var INVALID_CHARS_REGEX = /[\uFFFE\uFEFF\uFFFF\u200E\u200F\u202A-\u202E\x00-\x09\x0B\x0C\x0E-\x1F]/g,
RENDER_URLS_AS_PRETTY_LINKS = $.browser.mozilla && parseInt($.browser.version, 10) < 2,
TRAILING_SINGLE_SPACE_REGEX = / $/,
LINE_FEEDS_REGEX = /\r\n|\n\r|\n/g,
MAX_OFFSET = Number.MAX_VALUE
});
define("app/ui/compose/tweet_box_manager", ["module", "require", "exports", "app/ui/compose/tweet_box", "app/ui/compose/dm_composer", "app/ui/geo_picker", "core/component", "app/ui/compose/with_rich_editor"], function(module, require, exports) {
function tweetBoxManager() {
this.createTweetBoxAtTarget = function(a, b) {
this.createTweetBox(a.target, b)
}, this.createTweetBox = function(a, b) {
var c = $(a);
if (!((b.eventData || {}).scribeContext || {}).component) throw new Error("Please specify scribing component for tweet box.");
c.find(".geo-picker").length > 0 && GeoPicker.attachTo(c.find(".geo-picker"), b, {
parent: c
});
var d = c.find("div.rich-editor").length > 0 ? [withRichEditor] : [],
e = (b.dmOnly ? DmComposer : TweetBox).mixin.apply(this, d),
f = {
typeaheadData: this.attr.typeaheadData
};
e.attachTo(c, f, b)
}, this.after("initialize", function() {
this.on("uiInitTweetbox", this.createTweetBoxAtTarget)
})
}
var TweetBox = require("app/ui/compose/tweet_box"),
DmComposer = require("app/ui/compose/dm_composer"),
GeoPicker = require("app/ui/geo_picker"),
defineComponent = require("core/component"),
withRichEditor = require("app/ui/compose/with_rich_editor"),
TweetBoxManager = defineComponent(tweetBoxManager);
module.exports = TweetBoxManager
});
Obviously, this "answer" doesn't solve anything, but hopefully could provide enough to (re-)spark a conversation about this topic.
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