Javascript Variable Declaration With ||

I'm investigating Three.js at the moment and have come across this variable declaration at the top of the main source file: var THREE = THREE || { REVISION: '52' }; I'm just wonde

Solution 1:

The above means:

If the value of THREE evaluates to true, assign the value of THREE to the THREE variable, otherwise initialize it to the object { REVISION: '52' }.

Solution 2:

In code, it's like saying:

var THREE;
if (THREE) {
    THREE = { REVISION: '52' };
}
else {
    THREE = THREE;
}

Or:

var THREE = (THREE) ? { REVISION: '52' } : THREE;

Solution 3:

lazy instantiation. If the variable is declared already, then assign a value to it.