Encode strings by subtracting one from each character code

Question

I currently have this encoding function which simply subtracts one from each character code:

String.fromCharCode.apply(null, text.split("").map(function(v) {
 return v.charCodeAt() - 1;
}));

E.g. test becomes sdrs.

I know that this function is silly because it isn't a strong encoding algorithm, but that's not my point. The problem is that it is slow and causes a stack overflow for large strings (~130.000 in length).

I tried a regexp but that's even slower:

text.replace(/./g, function(v) {
 return String.fromCharCode(v.charCodeAt() - 1);
});

I tested both on jsPerf.

Currently, I'm executing a function for each character in both functions. How can I make a function that does the same thing as what these functions are doing, but executes faster without stack overflows?

Answer 1

Try looping through it with a simple for loop:

var b = '';
for (var i = 0; i < a.length; i++)
{
 b += String.fromCharCode(a.charCodeAt(i) - 1)
}
return b;

• pimvdb: Wow, that seems amazingly fast. More than 20 times as fast in fact. Thanks!