Approach 3: Loading JavaScript on demand

The JavaScript code for a page falls into two groups—code required to render the page, and code required to handle user interface events, such as button clicks. The code to render the page is used to make the page look better , and to attach event handlers to for example, buttons.

Although the rendering code needs to be loaded and executed in conjunction with the page itself, the user interface code can be loaded later, in response to a user interface event, such as a button click. That reduces the amount of code to be loaded, and therefore the time rendering of the page is blocked. It also reduces your bandwidth costs, because the user interface code is loaded only when it's actually needed.

On the other ...

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