My JSON looks like this
{\"rows\":[
{\"key\":[\"zeit.de\"],\"value\":98},
{\"key\":[\"google.com\"],\"value\":49},
{\"key\":[\"spiegel.de\"],\"value\
var json = '{"rows":[{"key":["zeit.de"],"value":98},{"key":["google.com"],"value":49},{"key":["spiegel.de"],"value":20},{"key":["spiegel.de"],"value":12},{"key":["spiegel.de"],"value":20},{"key":["spiegel.de"],"value":12},{"key":["netmng.com"],"value":49},{"key":["zeit.de"],"value":300}]}';
var obj = JSON.parse(json);
var newObj = {};
for(i in obj['rows']){
var item = obj['rows'][i];
if(newObj[item.key[0]] === undefined){
newObj[item.key[0]] = 0;
}
newObj[item.key[0]] += item.value;
}
var result = {};
result.rows = [];
for(i in newObj){
result.rows.push({'key':i,'value':newObj[i]});
}
console.log(result);
https://jsfiddle.net/s8rp84qc/