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, ''); 

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 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.

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;
}

<!-- Script provides the `snippet` object, see http://meta.stackexchange.com/a/242144/134069 -->
<script src="//tjcrowder.github.io/simple-snippets-console/snippet.js"></script>

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.

If you want to match ")" and "-" separately, use g flag

"File name) - Title".match(/[^ a-zA-Z\d\s:]/g)

If you want to match ") -" which is non-alphanumeric+space+non-alphanumeric,

"File name) - Title".match(/^ a-zA-Z\d\s:*[^ a-zA-Z\d\s:]/g)