JavaScript
var list = [{"_canUpsert":null,"_id":"task_82089805","email":null,"msg":"HTML","priority":0},{"_canUpsert":null,"_id":"task_25745709","email":null,"msg":"CSS","priority":"-8"},{"_canUpsert":null,"_id":"task_42914095","email":null,"msg":"WebDesign","priority":"3"},{"_canUpsert":null,"_id":"task_87257347","email":null,"msg":"LOL","priority":"1"},{"_canUpsert":null,"_id":"task_39654283","email":null,"msg":"thanks mike","priority":"12"},{"_canUpsert":null,"_id":"task_62483165","email":null,"msg":"poo haha ","priority":"-3"},{"_canUpsert":null,"_id":"task_45136691","email":null,"msg":"sdsdssd","priority":"30"},{"_canUpsert":null,"_id":"task_10733802","email":null,"msg":"new one","priority":"-7"},{"_canUpsert":null,"_id":"task_21176451","email":null,"msg":"another one","priority":"1992"},{"_canUpsert":null,"_id":"task_87979436","email":null,"msg":"test","priority":200},{"_canUpsert":null,"_id":"task_58382620","email":null,"msg":"testie","priority":"29"}];
list.forEach(function(data){data.priority = parseInt(data.priority,10);})
list.sort(function(a, b){return b.priority - a.priority;});
for (var i=0; i<list.length; i++)
console.log(list[i].priority)
//list.forEach(function(data){console.log(data.priority)});