What Are Global Variables? – It is a variable which has global scope and it is evident through the program unless shadowed.
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What Is the Difference Between Undefined and Null? – The variable value without a value is undefined – not initialised. Setting their value to null clears the variables. It is possible to test for each using the three equal signs or two equal signs. The null value uses force which could have odd results.
What is Event Bubbling? – This describes the performance of events in parent and child nodes in the Document Object Model (DOM). Parent nodes receive child node events. The advantage of this method is speed as the code only has to cross the DOM once. This will allow you to put more than a single event hearer on a DOM element as you can put one listener on all the components. This means code reduction and simplicity.