#JavaScript (ES7), 35 bytes

f=(n,d=n**.5)=>n%d?f(n,-~d):[d,n/d]

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###How?

If \$n\$ is a square, \$d=\sqrt{n}\$ is an integer which obviously divides \$n\$, so we immediately have an answer. Otherwise, the first -~d will act as \$\lceil{d}\rceil\$ and the next ones as \$d+1\$. Either way, we stop as soon as \$n\equiv 0\pmod{d}\$ which in the worst case (i.e. if \$n\$ is prime) happens when \$d=n\$.

JavaScript (ES7), 35 bytes

f=(n,d=n**.5)=>n%d?f(n,-~d):[d,n/d]

Try it online!

How?

If \$n\$ is a square, \$d=\sqrt{n}\$ is an integer which obviously divides \$n\$, so we immediately have an answer. Otherwise, the first -~d will act as \$\lceil{d}\rceil\$ and the next ones as \$d+1\$. Either way, we stop as soon as \$n\equiv 0\pmod{d}\$ which in the worst case (i.e. if \$n\$ is prime) happens when \$d=n\$.

#JavaScript (ES7), 35 bytes

f=(n,d=n**.5)=>n%d?f(n,-~d):[d,n/d]

Try it online!

###How?

If \$n\$ is a square, \$d=\sqrt{n}\$ is an integer and we immediately have an answer. Otherwise, the first -~d will act as \$\lceil{d}\rceil\$ and the next ones as \$d+1\$. Either way, we stop as soon as \$n\equiv 0\pmod{d}\$.

#JavaScript (ES7), 35 bytes

f=(n,d=n**.5)=>n%d?f(n,-~d):[d,n/d]

Try it online!

###How?

If \$n\$ is a square, \$d=\sqrt{n}\$ is an integer which obviously divides \$n\$, so we immediately have an answer. Otherwise, the first -~d will act as \$\lceil{d}\rceil\$ and the next ones as \$d+1\$. Either way, we stop as soon as \$n\equiv 0\pmod{d}\$ which in the worst case (i.e. if \$n\$ is prime) happens when \$d=n\$.