TypeScript generate strong password

strong-password.ts

function generateRandomSecret(length = 32): string {
    const haystacks = [
      "abcdefghijklmnopqrstuvwxyz",
      "ABCDEFGHIJKLMNOPQRSTUVWXYZ",
      "0123456789",
      "~`!@#$%^&*()_-+={[}]|\\:;\"'<,>.?/"
    ];
    const randomPart = (haystack: string, length: number)=>{
      let retVal = "";
      for (let i = 0, n = haystack.length; i < length; ++i) {
        retVal += haystack.charAt(Math.floor(Math.random() * n));
      }
      return retVal;
    }
    let retVal = ""
    haystacks.forEach((haystack)=>retVal+=randomPart(haystack, length/haystacks.length))

    const a = retVal.split("");
    const n = a.length;

    for(let i = n - 1; i > 0; i--) {
      const j = Math.floor(Math.random() * (i + 1));
      const tmp = a[i];
      a[i] = a[j];
      a[j] = tmp;
    }
    return a.join("").substring(0, length);
  }