You have one error that I can see on line 7. You are using the assignment operator instead of the equality operator in your if statement. You probably know this but if you want to compare two values you use either == or ===. This is an easy mistake to make.

if (vals[a][i] = today) {

should be:

if (vals[a][i] === today) {

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Assignment

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Equality

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Strict_equality