Using underscore

I would like to use this library more, so I'll collect how I have used it so far here...

Selecting objects from an array of objects:

var newArray = _.filter(array, function(e) {  
   return e.propertyName == search; 
});

Instead of a loop-solution, like:

var newArray = [];  
for (var i=0; i < array.length; i++) {  
   if (array[i].propertyName == search) {
      newArray.push(array[i]);
   }
}
return newArray;  

If we have two arrays with the same type of objects and we want all objects in one array, except if they are in the second array:

// We have two arrays with the same types of objects.
// We want an array with the objects in array 1, except if the object exists in array 2.
resultArray = _.filter(array1, function(elementArray1) {  
    return !_.find(array2, function(elementArray2) {
        return elementArray1.propertyName === elementArray2.propertyName;
    });
});

If we want an array of ids (or some other property) from an array of objects:

var ids = _.pluck(array, "id");  
}