Use RegEx / /g with replace() method to Javascript replace all spaces. The flag g means global. It causes all matches to be replaced.
replaceSpace.replace(/ /g, "");Pure Javascript, without regular expression:
var result = replaceSpacesText.split(" ").join("");Javascript replaces all spaces
A simple example code replaces all white spaces with -:
<!DOCTYPE html>
<html>
<body>
<script>
let myString = "The dog has a long tail, and it is RED!"
var res = myString.replace(/ /g,"-")
console.log(res)
var out = myString.replace(/ /g,"")
console.log(out)
</script>
</body>
</html>Output:

Regex to replace multiple spaces with a single space
Just replace \s\s+ with ' ':
<script>
let str = "The dog has a long tail, and it is RED!"
var res = str.replace(/\s\s+/g, ' ');
console.log(res)
</script>Output: The dog has a long tail, and it is RED!
Replace all spaces in a string with ‘+’
var str = 'a b c';
var replaced = str.split(' ').join('+');var str = 'a b c';
var replaced = str.replace(/\s/g, '+');Do comment if you have any doubts or suggestions on this Js replace topic.
Note: The All JS Examples codes are tested on the Firefox browser and the Chrome browser.
OS: Windows 10
Code: HTML 5 Version