在javascript中将任何字符串转换为数组的最快方法

Question

I'm currently developing a GameBoyColor emulator in Javascript.

Loading a 64k ROM file into the Memory Unit takes about 60 seconds right now. This is the function:

loadROM: function (file) {
    var reader = new FileReader();

    reader.onload = function () {
        var start = new Date();
        console.log("start", start.getTime());

        this.__ROM = new Uint8Array(reader.result.length);

        for (var i = 0; i < reader.result.length; i++) {
            this.__ROM[i] = (reader.result.charCodeAt(i) & 0xFF);
        }

        var end = new Date();
        console.log("end", end.getTime());

        console.log((end.getTime() - start.getTime()) + " for " + i + " iterations");

        this._trigger("onROMLoaded");
    }.context(this);

    reader.readAsBinaryString(file);
}

reader.result is the ROM file as string and this.__rom is the array. Important is the for loop where I get every single character and push it to the ROM array of the memory.

This takes way to long. So question is how to speed this thing up. Is there any better approach to convert a string into an array?

Answer 1

You should be able to do it natively using split() instead of looping:

// See the delimiter used
this.__ROM = reader.result.split('');

// And to do the bitwise AND on each byte, use map()
this.__ROM = this.__ROM.map(function(i) {
    return i & 0xFF;
});

Or in one step (without writing to this.__ROM twice):

this.__ROM = reader.result.split('').map(function(i) {
    return i & 0xFF;
});