Simple chessboard-generating script from Eloquent JavaScript Chapter 2.

chessboard.js

var size = 15, base = "";

for(var i = 1; i <= size; i++) {
    if(i % 2 === 1) {
        for(var k = 1; k <= size; k++) {
            if(k % 2 === 1) {
                base += "#";
            } else {
                base += " ";
            }
        }
    } else {
        for(var k = 1; k <= size; k++) {
            if(k % 2 === 1) {
                base += " ";
            } else {
                base += "#";
            }
        }
    }

    if(i < size) {
        base += "\n";
    }
}

console.log(base);