normalize.ts

const str = '   some      string  ';

function normalize(input: string): string {
  let length = input.length;
  let i = 0;
  
  while (i < length - 1) {
    const char: string = input[i];
    const nextChar: string = input[i + 1];
        
    if (char === ' ' && nextChar === ' ') {
      input = input.substr(0, i) + ' ' + input.substr(i + 2);

      length - 1;
      continue;
    }
    
    i++;
  }
  
  return input;
}

console.log(normalize(str));