Variable not visible inside for loop

Question

I have a for loop in JavaScript like

var loopvariable = 0;  
let row = [[]];
for (var key in supplies.food) {
     row[loopvariable][0] = key;
     row[loopvariable][1] = supplies.food[key];
     loopvariable++;
}

why am i getting the following error

TypeError: row[loopvariable] is undefined

Answer 1

The variable

row[loopvariable]

is not initialized. You could use a default value and take an array with a guard operator (logical OR ||).

row[loopvariable] = row[loopvariable] || [];

A shorter approach could be just to push a new array to row, without using an aditional variable loopvariable

let row = [];
for (var key in supplies.food) {
    row.push([key, supplies.food[key]]);
}