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When you visit a website, your browser sends a request to the site’s server. The server then sends back the HTML code for the page, which your browser renders as a webpage. The HTML code includes instructions called “scripts” that tell your browser how to do things, such as display images or run interactive content.
let x = 42
Runtime errors are usually more difficult to debug because they can occur anywhere in your program. A runtime error is caused by attempting to access a variable that does not exist or by invoking a function that is not defined. For example, the following line of code causes a runtime error because it attempts to invoke the undefined function myFunction() :