Remove all special characters except space from a string using JavaScript

You should use the string replace function, with a single regex. Assuming by special characters, you mean anything that's not letter, here is a solution:

const str = "abc's test#s";
console.log(str.replace(/[^a-zA-Z ]/g, ""));

You can do it specifying the characters you want to remove:

string = string.replace(/[&\/\\#,+()$~%.'":*?<>{}]/g, '');

Alternatively, to change all characters except numbers and letters, try:

string = string.replace(/[^a-zA-Z0-9]/g, '');

The first solution does not work for any UTF-8 alphabet. (It will cut text such as Привіт). I have managed to create a function which does not use RegExp and use good UTF-8 support in the JavaScript engine. The idea is simple if a symbol is equal in uppercase and lowercase it is a special character. The only exception is made for whitespace.

function removeSpecials(str) {
    var lower = str.toLowerCase();
    var upper = str.toUpperCase();

    var res = "";
    for(var i=0; i<lower.length; ++i) {
        if(lower[i] != upper[i] || lower[i].trim() === '')
            res += str[i];
    }
    return res;
}

Update: Please note, that this solution works only for languages where there are small and capital letters. In languages like Chinese, this won't work.

Update 2: I came to the original solution when I was working on a fuzzy search. If you also trying to remove special characters to implement search functionality, there is a better approach. Use any transliteration library which will produce you string only from Latin characters and then the simple Regexp will do all magic of removing special characters. (This will work for Chinese also and you also will receive side benefits by making Tromsø == Tromso).

I don't know JavaScript, but isn't it possible using regex?

Something like [^\w\d\s] will match anything but digits, characters and whitespaces. It would be just a question to find the syntax in JavaScript.

search all not (word characters || space):

str.replace(/[^\w ]/, '')