JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" value="" id="res" />

JavaScript

var calendar=[[1, "49", 2], [1, "49", 1], [2, "50", 7], [2, "50", 5], [2, "51", 2], [2, "51", 5]];

var recap={}
var elt=-1;
while(calendar[++elt]){
    
    idx= calendar[elt][0].toString();

    
    if (!recap[idx]){
               recap[idx]={};
               }
    
    if (!recap[idx][calendar[elt][1]]){
        console.log('new')
        recap[idx][calendar[elt][1]]=calendar[elt][2]
    
    }
    else { 
               recap[idx][calendar[elt][1]]=recap[idx][calendar[elt][1]]+calendar[elt][2]
    }
}

function showTotalUserperWeek(u,w){
document.getElementById('res').value=recap[u][w]
}

//id user 2 Semaine 51 ...
 showTotalUserperWeek('2','51');