A one-line JavaScript function that merges two objects.

mergeObjects.js

/**
*   Merge two objects. Warning: this function permanently changes obj1 due to it being passed by reference. 
*   If a property/method exists in both objects obj2's will overwrite the value that existed in obj1.
*   @param obj1 The object to merge into.
*   @param obj2 An object with properties to add to obj1.
*   @return NULL
**/
function mergeObjects(obj1, obj2)
{
    Object.keys(obj2).forEach(function(key) { obj1[key] = obj2[key]; });
}