Need to determine if two physical points on a map are within a certain number of statute miles of each other? I got you covered.

withinRange.js

function withinRange(sourceLong, sourceLat, targetLong, targetLat, range) {
    var nauticalMilesPerStatuteMile = 0.868976;
    // Latitude is always the same distance. Divide degrees by 60 to get arcminutes
    var milesPerMinLat = 69.047 / 60;
    // Distance in miles per arcminute longitude depends on the cosine of the arcminutes of latitude
    var milesPerMinLong = (1 * Math.cos(sourceLat)) / nauticalMilesPerStatuteMile;
    // Get delta in minutes between source and target longitude, convert to statute miles
    var deltaLong = Math.abs((sourceLong * 60) - (targetLong * 60));
    // Convert `deltaLong` to statute miles, rounding to 2 decimal places
    var deltaLong = Math.round((milesPerMinLong * deltaLong) * 100) / 100;
    // Get delta in minutes between source and target latitude, convert to statute miles
    var deltaLat = Math.abs((sourceLat * 60) - (targetLat * 60));
    // Convert `deltaLat` to statute miles, rounding to 2 decimal places
    var deltaLat = Math.round((milesPerMinLat * deltaLat) * 100) / 100;
    // Get combined delta of the lat/long pairs by finding the long
    // edge of the triangle formed by the intersection of the deltas
    // Yay math!: deltaLong**2 + deltaLat**2 == delta**2
    var delta = Math.sqrt(Math.pow(deltaLong, 2) + Math.pow(deltaLat, 2));
    // Return true if the delta is less than or equal to `range`, else return false
    return delta <= range;
}