A 'for' loop variable declared with 'var' is captured in closures

The array funcs is filled with 10 closures in a for loop. The closures capture the loop variable 'i', which is declared with keyword var. Each closure simply returns the captured variable:

var funcs = [], sum=0;

for(var i=0; i < 10; ++i) {
  funcs.push(function() {
    return i;  
  });
}

The closures are called in a loop to calculate the sum of their returned values:

for(var j=0; j < funcs.length; ++j)
 sum += funcs[j]();

What will be the value of sum?

console.log(sum);