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Search for full word instead of part inside of it

I'm trying to find exact word in text user is sending, but obviously, when I'm trying to use message.content.includes(), it's also looking for parts of the word in text which I don't need! Any way to search by full words only?
Few examples: **TexT**, HeLlO, etc.

Yes, you can use a regex like this, assuming wordToFind holds the word you are searching for:
// Create regex from word with \b at each end which
// means "word boundary", and the 'i' option means
// case-insensitive
const wordSearch = new RegExp(`\b${wordToFind}\b`, 'i');
// Use the regular expression to test the content:
const hasWord = wordSearch.test(message.content);
// will be true if whole word is found

Put your content in to an array, splitting words if it's a piece of text. Array.includes will match whole words.
So either use [content].includes(word) if content is a single word, or content.split(' ').includes(word) if content is multiple words.

Replace words of text area

I have made a javascript function to replace some words with other words in a text area, but it doesn't work. I have made this:
function wordCheck() {
var text = document.getElementById("eC").value;
var newText = text.replace(/hello/g, '<b>hello</b>');
document.getElementById("eC").innerText = newText;
}
When I alert the variable newText, the console says that the variable doesn't exist.
Can anyone help me?
Edit:
Now it replace the words, but it replaces it with <b>hello</b>, but I want to have it bold. Is there a solution?

Update:
In response to your edit, about your wanting to see the word "hello" show up in bold. The short answer to that is: it can't be done. Not in a simple textarea, at least. You're probably looking for something more like an online WYSIWYG editor, or at least a RTE (Richt Text Editor). There are a couple of them out there, like tinyMCE, for example, which is a decent WYSIWYG editor. A list of RTE's and HTML editors can be found here.
First off: As others have already pointed out: a textarea element's contents is available through its value property, not the innerText. You get the contents alright, but you're trying to update it through the wrong property: use value in both cases.
If you want to replace all occurrences of a string/word/substring, you'll have to resort to using a regular expression, using the g modifier. I'd also recommend making the matching case-insensitive, to replace "hello", "Hello" and "HELLO" all the same:
var txtArea = document.querySelector('#eC');
txtArea.value = txtArea.value.replace(/(hello)/gi, '<b>$1</b>');
As you can see: I captured the match, and used it in the replacement string, to preserve the caps the user might have used.
But wait, there's more:
What if, for some reason, the input already contains <b>Hello</b>, or contains a word containing the string "hello" like "The company is called hellonearth?" Enter conditional matches (aka lookaround assertions) and word boundaries:
txtArea.value = txtArea.value.replace(x.value.replace(/(?!>)\b(hello)\b(?!<)/gi, '<b>$1</b>');
fiddle
How it works:
(?!>): Only match the rest if it isn't preceded by a > char (be more specific, if you want to and use (?!<b>). This is called a negative look-ahead
\b: a word boundary, to make sure we're not matching part of a word
(hello): match and capture the string literal, provided (as explained above) it is not preceded by a > and there is a word boundary
(?!<): same as above, only now we don't want to find a matching </b>, so you can replace this with the more specific (?!<\/b>)
/gi: modifiers, or flags, that affect the entire pattern: g for global (meaning this pattern will be applied to the entire string, not just a single match). The i tells the regex engine the pattern is case-insensitive, ie: h matches both the upper and lowercase character.
The replacement string <b>$1</b>: when the replacement string contains $n substrings, where n is a number, they are treated as backreferences. A regex can group matches into various parts, each group has a number, starting with 1, depending on how many groups you have. We're only grouping one part of the pattern, but suppose we wrote:
'foobar hello foobar'.replace(/(hel)(lo)/g, '<b>$1-$2</b>');
The output would be "foobar <b>hel-lo</b> foobar", because we've split the match up into 2 parts, and added a dash in the replacement string.
I think I'll leave the introduction to RegExp at that... even though we've only scratched the surface, I think it's quite clear now just how powerful regex's can be. Put some time and effort into learning more about this fantastic tool, it is well worth it.

If <textarea>, then you need to use .value property.
document.getElementById("eC").value = newText;
And, as mentioned Barmar, replace() replaces only first word. To replace all word, you need to use simple regex. Note that I removed quotes. /g means global replace.
var newText = text.replace(/hello/g, '<b>hello</b>');
But if you want to really bold your text, you need to use content editable div, not text area:
<div id="eC" contenteditable></div>
So then you need to access innerHTML:
function wordCheck() {
var text = document.getElementById("eC").innerHTML;
var newText = text.replace(/hello/g, '<b>hello</b>');
newText = newText.replace(/<b><b>/g,"<b>");//These two lines are there to prevent <b><b>hello</b></b>
newText = newText.replace(/<\/b><\/b>/g,"</b>");
document.getElementById("eC").innerHTML = newText;
}

Remove string after predefined string

I am pulling content from an RSS feed, before using jquery to format and edit the rss feed (string) that is returned. I am using replace to replace strings and characters like so:
var spanish = $("#wod a").text();
var newspan = spanish.replace("=","-");
$("#wod a").text(newspan);
This works great. I am also trying to remove all text after a certain point. Similar to truncation, I would like to hide all text starting from the word "Example".
In this particular RSS feed, the word example is in every feed. I would like to hide "example" and all text the follows that word. How can I accomplish this?

Though there is not enough jQuery, you even don't need it to remove everything after a certain word in the given string. The first approach is to use substring:
var new_str = str.substring(0, str.indexOf("Example"));
The second is a trick with split:
var new_str = str.split("Example")[0];

If you also want to keep "Example" and just remove everything after that particular word, you can do:
var str = "aaaa1111?bbb&222:Example=123456",
newStr = str.substring(0, str.indexOf('Example') + 'Example'.length);
// will output: aaaa1111?bbb&222:Example

jQuery isn't intended for string manipulation, you should use Vanilla JS for that:
newspan = newspan.replace(/example.*$/i, "");
The .replace() method accepts a regular expression, so in this case I've used /example.*$/i which does a case-insensitive match against the word "example" followed by zero or more of any other characters to the end of the string and replaces them with an empty string.

I would like to hide all text starting from the word "Example"
A solution that uses the simpler replace WITH backreferences so as to "hide" everything starting with the word Example but keeping the stuff before it.
var str = "my house example is bad"
str.replace(/(.*?) example.*/i, "$1") // returns "my house"
// case insensitive. also note the space before example because you
// probably want to throw that out.

replacing spaces in a string with hyphens

I have a string and I need to fix it in order to append it to a query.
Say I have the string "A Basket For Every Occasion" and I want it to be "A-Basket-For-Every-Occasion"
I need to find a space and replace it with a hyphen. Then, I need to check if there is another space in the string. If not, return the fixed string. If so, run the same process again.
Sounds like a recursive function to me but I am not sure how to set it up. Any help would be greatly appreciated.

You can use a regex replacement like this:
var str = "A Basket For Every Occasion";
str = str.replace(/\s/g, "-");
The "g" flag in the regex will cause all spaces to get replaced.
You may want to collapse multiple spaces to a single hyphen so you don't end up with multiple dashes in a row. That would look like this:
var str = "A Basket For Every Occasion";
str = str.replace(/\s+/g, "-");

Use replace and find for whitespaces \s globally (flag g)
var a = "asd asd sad".replace(/\s/g,"-");
a becomes
"asd-asd-sad"

Try
value = value.split(' ').join('-');
I used this to get rid of my spaces. Instead of the hyphen I made it empty and works great. Also it is all JS. .split(limiter) will delete the limiter and puts the string pieces in an array (with no limiter elements) then you can join the array with the hyphens.

JavaScript regexp get a word between texts

In javascript I need to get the text within the custom tag. For example
[tag_retweet attr="val" attr2="val"]
In this case I need to get the word "retweet" only skipping all other texts and another example is,
[tag_share]
Here I need to get the word "share".
So what will be the regexp for getting that tag name in my case ??

Something like /\[tag_([a-z0-9_]+)(?:\s+|\])/
var tag = '[tag_retweet attr="val" attr2="val"]';
var match = tag.match(/\[tag_([a-z0-9_]+)(?:\s+|\])/);
window.alert(match[1]);​ // alerts "retweet"

The regex to capture it would be:
/.*\[tag_(.*?)\W.*/
This matches any characters up to the end of [tag_ and then starts capturing any caracters until it encounters a non-word character, then any other characters. The match will contain only the releavant parts.
use it like:
myString.match(/.*\[tag_(.*?)\W.*/)[1]

Basically, you're looking for what comes after [tag_, up until the next space (or the end of the tag)
So:
var tag = '[tag_retweet attr="val" attr2="val"]';
// or var tag = '[tag_share]';
var match = tag.match(/\[tag_(.*?)[\] ]/)[1];