function (param1) {
params1 = !params1 && params1 !== 0 ? 1 : param1; (if param1 not set and is not 0 --> set it to default value else --> param1
....
}
function fn (param1){
var myParam = param1 || defaultValue;
//creates a new variable param with either param1 as value or, if param1 is undefined, defaultValue
}