Idiomatic way to set default value in javascript
What would be the most idiomatic way to do the following in javascript:
If myParam is not passed into MyFunc by the caller, then I want to set it to a default value. But first I want to try and get it from another object, which may not yet exist:
function MyFunc(myParam) {
if (!myParam) {
if (!myObj) {
myParam = 10;
}
else {
myParam = myObj.myParam;
}
}
alert(myParam);
}
I started to write:
myParam = myParam || myObj.mParam || 10
but realized that if myObj does not exist then this would fail. I might guess the following:
myParam = myParam || (myObj && myObj.mParam) || 10
It might even work. But is it the best way?
How would for example John Resig do it?
If myObj is a global it needs to reference the window object, otherwise it will throw an error if myObj is undefined.
myParam = myParam || (window.myObj ? window.myObj.mParam : 10);
or
myParam = myParam || (window.myObj && window.myObj.mParam) || 10;
This works as well:
myParam = myParam || ((typeof myObj !== "undefined") ? myObj.mParam : 10);
I think the other answers have proven that there are a whole bunch of ways a one-liner can fail here. My version below is perhaps more readable, and doesn't explicitly test for object/property existence, but isn't much shorter:
function MyFunc(myParam){
if (!myParam){
try{
myParam = myObj.myParam;
}
catch(e){
myParam = 10;
}
}
}