js 数组转json

var json="[";
for(var i=0;i<cart.length;i++){
json+="[";
for(var j=0;j<cart[i].length;j++){
if(j<cart[i].length-1){
json+="\""+cart[i][j]+"\",";
}else{
json+="\""+cart[i][j]+"\"";
}
}
if(i<cart.length-1){
json+="],";
}else{
json+="]";
}
}
json+="]";