JSFiddle - React, Tailwind, and code Playground

JavaScript

var final = {
    1: {
        score:0
    },
    
    2: {
        score: 2
    },
    
    3: {
        score: 0
    },
    
    4: {
        score: 5   
    },
    
    5: {
        score: 1
    },
    
    6: {
        score: 10
    },
    
    7: {
        score: 10
    }
},

ya = {
   
    2: {
        score: 2
    },
    
    10: {
        score: 3
    },
    
    4: {
        score: 0   
    },
    
    15: {
        score: 0
    },
    
    6: {
        score: 4
    },
    
    17: {
        score: 5
    }
}; 

for (var i in ya) {
    final[i] = final[i] || {score: 0};
    final[i].score += ya[i].score;
}

document.body.innerHTML = JSON.stringify(final);