Be aware, that \W leaves the underscore. A short equivalent for [^a-zA-Z0-9] would be [\W_]

text.replace(/[\W_]+/g," ");

\W is the negation of shorthand \w for [A-Za-z0-9_] word characters (including the underscore)

Example at regex101.com

This is actually fairly straightforward.

Assuming str is the string you're cleaning up:

str = str.replace(/[^a-z0-9+]+/gi, '+');

The ^ means "anything not in this list of characters". The + after the [...] group means "one or more". /gi means "replace all of these that you find, without regard to case".

So any stretch of characters that are not letters, numbers, or '+' will be converted into a single '+'.

To remove parenthesized substrings (as requested in the comments), do this replacement first:

str = str.replace(/\(.+?\)/g, '');

function replacer() {

  var str = document.getElementById('before').value.
    replace(/\(.+?\)/g, '').
    replace(/[^a-z0-9+]+/gi, '+');

  document.getElementById('after').value = str;
}

document.getElementById('replacem').onclick = replacer;

<p>Before:
  <input id="before" value="Durarara!!x2 Ten" />
</p>

<p>
  <input type="button" value="replace" id="replacem" />
</p>

<p>After:
  <input id="after" value="" readonly />
</p>

Remove the space from the first set and will do the job:

name.replace(/[^0-9a-zA-Z]/g, '');

You may read this code as "remove all characters that are not digits ([0-9]) and alpha characters ([a-zA-Z])".

Alternatively, you can use the i flag to make your regular expression ignore case. Then the code can be simplified:

name.replace(/[^0-9a-z]/gi, ''); 

Apparently, there is a way to do this with one line

You can use grouping identifiers in your replacements string like this:

'<foo>Some data</foo>'.replace(/(<foo>)(.+)(<\/foo>)/,'<bar>$2</bar>')

However, at the end of the day, if you ONLY want to replace closing tags, just replace those, don't worry about the rest of the content, unless you need to pass that through as well. If you are only looking at ... then this is the expression you need:

/<\/content>.+<\/message>/

You can use a negated character class:

var temp = originalname.replace(/[^\w.]+/g, "_");

[^\w.]+ will match 1 or more of any character that is not a word character and not a DOT.

this.colorPreset1=this.colorPreset1.replace(/[^0-9a-zA-Z]/g, '');

The character group was changed to a exclusion group. [^] will match any character not in the list. As you had it, it would only match the characters you wanted to keep.

The anchors for the string were removed - You're wanting to replace any non-alpha numeric characters, so it doesn't matter where they're located.

The global flag //g was added so it will replace all matches instead of just the first one.

You're using toLowerCase when creating strReverse, and then comparing it with str. But str will still have upper-case characters in it. Additionally, you're leaving the non-alpha characters in str.

You also need to remove _ for the last one to work, which \W won't do on its own.

You need to first prep str, then create the reversed version of it, and do the check:

function palindrome(str) {
    var strReverse;
    str = str.toLowerCase().replace(/\W|_+/g,'');
    strReverse = str.split('').reverse().join('');
    return strReverse === str;
}

Live Example:

function palindrome(str) {
    var strReverse;
    str = str.toLowerCase().replace(/\W|_+/g,'');
    strReverse = str.split('').reverse().join('');
    return strReverse === str;
}
function test(str, expectedResult) {
    var result = palindrome(str);
    var p = document.createElement('p');
    p.className = !result == !expectedResult ? "good" : "bad";
    p.appendChild(document.createTextNode(str));
    document.body.appendChild(p);
}
test("eye", true);
test("race car", true);
test("not a palindrome", false);
test("A man, a plan, a canal. Panama", true);
test("never odd or even", true);
test("nope", false);
test("almostomla", false);
test("My age is 0, 0 si ega ym.", true);
test("1 eye for of 1 eye.", false);
test("0_0 (: /-\ :) 0-0", true);

.good {
  color: green;
}
.bad {
  color: #d00;
}

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Removing non-alphanumeric chars

The following is the/a correct regex to strip non-alphanumeric chars from an input string:

input.replace(/\W/g, '')

Note that \W is the equivalent of [^0-9a-zA-Z_] - it includes the underscore character. To also remove underscores use e.g.:

input.replace(/[^0-9a-z]/gi, '')

The input is malformed

Since the test string contains various escaped chars, which are not alphanumeric, it will remove them.

A backslash in the string needs escaping if it's to be taken literally:

"\\test\\red\\bob\\fred\\new".replace(/\W/g, '')
"testredbobfrednew" // output

Handling malformed strings

If you're not able to escape the input string correctly (why not?), or it's coming from some kind of untrusted/misconfigured source - you can do something like this:

JSON.stringify("\\test\red\bob\fred\new").replace(/\W/g, '')
"testredbobfrednew" // output

Note that the json representation of a string includes the quotes:

JSON.stringify("\\test\red\bob\fred\new")
""\\test\red\bob\fred\new""

But they are also removed by the replacement regex.

You can use [\W_] to get rid of characters that are not alphanumeric. Where W represent characters from a-z, A-Z and 0-9

var str = 'this $is a _test@#$%';
str = str.replace(/[\W_]+/g,' ');
console.log(str);

So, to make the words capitalise alongside the replace you can do,

var str = 'this $is a _test@#$%';
str = str.replace(/[\W_]+/g,' ');
var res = str.split(' ').map((s) => s.charAt(0).toUpperCase() + s.substr(1)).join(' ');
console.log(res);