Big O of javascript built-in split function

Question

Example:

var string = "abcde";
var array = string.split("");
// array = ["a", "b", "c", "d", "e"]

What is the amortized running time of this split function? Also, how do I view source code of such built-in functions in javascript?

Answer 1

With an empty delimiter argument, split is essentially equivalent to:

var len = string.length;
var result = Array(len)
for (i = 0; i < len; i++) {
    result[i] = string[i];
}

This is O(len).

With a delimiter, it becomes O(string.length * delimiter.length), because at each step in the loop it has to test whether there's a match for delimiter.