Please solve in typescript

Write a function solution that, given a string $S$ consisting of $N$ letters $\text{'}$a$\text{'}$ and$/$or $\text{'}$b$\text{'}$ returns true when all occurrences of letter $\text{'}$a$\text{'}$ are before all occurrences of letter $\text{'}$b$\text{'}$ and returns false otherwise.

Examples:

Given $S=$ "aabbb", the function should return true.

Given $S="$ba$",$ the function should return false.

Given $S=$ "aaa", the function should return true. Note that $\text{'}$b$\text{'}$ does not need to occur in S $.$

Given $S="$b$",$ the function should return true. Note that $\text{'}$a$\text{'}$ does not need to occur in S $.$

Given $S=$ "abba", the function should return false.

Write an efficient algorithm for the following assumptions:

N is an integer within the range $[1.\mathrm{.}300,000]$;

string $S$ is made only of the characters $\text{'}$a$\text{'}$ and$/$or $\text{'}$b$\text{'}.$