How to set the default value of JS custom function_javascript skills

If you want to set the default value of a to 5, you cannot write it as:
function my(a=5){

　xxx;

}


Simple After checking, there are the following ones that can be used:

function my(a){
　alert(a||5);
}

function my(a){
　a = typeof(a) == 'undefined' ? 5 : a;
}

function my(a){
　if(typeof(a) == 'undefined') {

　a = 5;

　}
}

Personally, I think the second one is more concise and clearer.