stringToBytes JavaScript Performance
Searching for a simple function to convert javascript strings to byte arrays, I stumbled over this stackoverflow answer.
While it’s implementation is correct, it has a significant performance problem. For large strings, the internal byte array is recreated too often. It’s somewhat similar to using the += operator on strings in java instead of using a StringBuilder. A faster function is below.
function stringToBytesFaster ( str ) {
var ch, st, re = [], j=0;
for (var i = 0; i < str.length; i++ ) {
ch = str.charCodeAt(i);
if(ch < 127)
{
re[j++] = ch & 0xFF;
}
else
{
st = []; // clear stack
do {
st.push( ch & 0xFF ); // push byte to stack
ch = ch >> 8; // shift value down by 1 byte
}
while ( ch );
// add stack contents to result
// done because chars have "wrong" endianness
st = st.reverse();
for(var k=0;k<st.length; ++k)
re[j++] = st[k];
}
}
// return an array of bytes
return re;
}
To round up things, you can start a performance test here: clickme
Example output on Firefox 8, core2duo and strlength = 10000: Old: 2021ms New: 4ms Speedup factor:505.25
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