Pass values to javascript array filter?

Question

How can one pass a variable to a filter function in javascript?

In this case I'm trying to pass a value to variable "maxage":

var dateFilter = function(value,maxage) { // Age in miliseconds
    if(Date.now() - value < maxage) {
        return value;
        } else {
        return false;
        }
    }

    dates.filter(dateFilter,500);

How can I pass the value 500 to the filter as maxage?

Answer 1

You would need to invoke Function.prototype.bind to create something similar to a default argument.

dates.filter(dateFilter.bind( null, 500 ));

dateFilter callback would then called with 500 PLUS "automatic passed in values" value, index, array.

function dateFilter( customArgument, value, index, array ) {
    // customArgument === 500
}

Answer 2

maxage has been bound to this. Consider the following:

var dateFilter = function(value) {
  if(value < this) return value;
}
var dates = [1,2,3];
console.log(dates.filter(dateFilter,2));
> [1] // Output.

The MDN documentation shows the filter signature to be array.filter(callback[, thisObject])