charAt.js

// Explaining https://twitter.com/mcbazon/status/236504096868286464

// I have a simple output stream implementation that keeps track
// of current line/col numbers.  It accumulates text in the OUTPUT
// variable, and at times I needed to know the last character
// that was added.  I had this function:

function last_char() {
    return OUTPUT.charAt(OUTPUT.length - 1);
};

// Noticed that it was really slow in Chrome when the output got to
// about 200K.  Changing it to:

function last_char() {
    return last.charAt(last.length - 1);
}

// where in `last' I'm storing just the previously added chunk
// made it about 10 times faster (0.2s instead of 2.6s).
// tested with V8 (NodeJS v0.7.10-pre)

// according to my benchmark at http://jsperf.com/string-charat-length
// FF doesn't seem to exhibit the "long string problem" and it's also much
// faster overall.