gistfile1.js

function make() {
    var text = "";
    var possible = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";

    for( var i=0; i < 25; i++ )
        text += possible.charAt(Math.floor(Math.random() * possible.length));

    return text;
}

var arr = [];
for(var i=0; i<20000; i++) {
    arr.push(make());
}