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What is the difference between "hello".indexOf("") and "hello".indexOf("h")?

Gonzales

I am currently learning JavaScript where I found a problem that is confusing me. I tried to test "hello".indexOf("h") and the output showed 0 which is logical. However, when I tried this "hello".indexOf("") , the output showed 0 . How can an empty string's index is as same as the first letter?