Replace multiple characters in one replace call

If you want to replace multiple characters you can call the String.prototype.replace() with the replacement argument being a function that gets called for each match. All you need is an object representing the character mapping that you will use in that function.

For example, if you want a replaced with x, b with y, and c with z, you can do something like this:

const chars = {'a':'x','b':'y','c':'z'};
let s = '234abc567bbbbac';
s = s.replace(/[abc]/g, m => chars[m]);
console.log(s);

Output: 234xyz567yyyyxz

Use the OR operator (|):

var str = '#this #is__ __#a test###__';
str.replace(/#|_/g,''); // result: "this is a test"

You could also use a character class:

str.replace(/[#_]/g,'');

Fiddle

If you want to replace the hash with one thing and the underscore with another, then you will just have to chain. However, you could add a prototype:

String.prototype.allReplace = function(obj) {
    var retStr = this;
    for (var x in obj) {
        retStr = retStr.replace(new RegExp(x, 'g'), obj[x]);
    }
    return retStr;
};

console.log('aabbaabbcc'.allReplace({'a': 'h', 'b': 'o'}));
// console.log 'hhoohhoocc';

Why not chain, though? I see nothing wrong with that.