Access an object value using a key in a variable

Question

I have an object like this one (simplified version):

var currentDepartment = 'development';

var departments = {
    "development":{
        "name":"Development",
        "number":"100"
    },
    "marketing":{
        "name":"Marketing",
        "number":"101"
    }
}

I know that if I want to access to the number I have to so something like var number = departments.development.number or var number = departments.marketing.number. But what if I can't hardcode the department name?

Something like, I should not write development or marketing directly, instead, I need to get the number of the department with the code in the variable currentDeparment.