javascript replace regex spaces and newlines

how to replace spaces and newlines together with additional closing code ; in javascript?

function main(){
   var a = 'hello'
   console.log(a)
}

console.log(main.toString().replace(/[\n ]/g,''))

output

functionmain(){vara='hello'console.log(a)}

I want

function main(){var a='hello';console.log(a);}

maybe this is correct
<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

function removeSpaces(str){
        str = str.replace(/[\n]/g,';')
    let res = str.replace(/[\n ;]/g,(e, i)=>{
       switch(e){
         case ';':
           if(!'{:['.includes(str.substr(0, i).slice(-1))){
             return ';'
           }
        default:
          let arr = str.substr(0, i).split(' ')
          let lastArr = arr[arr.length - 1]
          // need space code
          if(['function','var','let','const'].includes(lastArr)){
             return ' '
          }
          return ''
        }
     })
    return res;
}
function main(){
   var a = 'hello'
   console.log(a)
}

let str = main.toString()
console.log(str.replace(/[\n ]/g,''))
let res = removeSpaces(str)
console.log(res) // function main(){var a='hello';console.log(a);}

<!-- end snippet -->

Based on your requirements, I think this regex can do the job:

/(?:(?<![\{\}])[\n]|([\{\}\;])(\n)|\b\s\B|\B\s\b|\B\s\B)/g

1- part one :

 (?<![\{\}])[\n] -> matches ending of statements without ;

2- part two:

 ([\{\}\;])(\n) -> matches newlines after { or } or ;

3- part three:

 \b\s\B|\B\s\b|\B\s\B ->match white spaces

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

function main() {
    var a = "hello"
    console.log(a)
    return 1;
  }
  
const result = main.toString().replaceAll(
  /(?:(?<![\{\}])[\n]|([\{\}\;])(\n)|\b\s\B|\B\s\b|\B\s\B)/g,
  function (match, p1) {
    if (match === "\n") return ";";
    if (match === " ") return "";
    return p1;
  }
);

console.log(result);

<!-- end snippet -->