function repeat(str, n){
var result = "";
for(var i = 0;i < n;i++){
result += str;
}
return result;
}
function includes(str, char){
return str.indexOf(char) !== -1;
}
function startsWith(str, char){
return str.indexOf(char) === 0;
}
function endsWith(str, char){
return !!str.match(new RegExp(char + "$"));
}