Difference between Javascript in Head and Body

Key difference: JavaScript is an interpreted computer programming language. It is a prototype-based scripting language that is dynamic, weakly typed, and has first-class functions. While embedding JavaScript on a webpage, it may appear almost anywhere within the HTML file. However, the code is usually written either under the head tag or the body tag. Usually, the code is placed in the head element. However, it is recommended that if the JavaScript is not required to be executed at the beginning of the page, it should be place at the bottom, in the body.

Even though their names suggest that Java and JavaScript must be related somehow, it is just not true. JavaScript is an interpreted computer programming language. The main difference between Java and JavaScript is that while Java is a programming language, JavaScript is scripting language. It is a prototype-based scripting language that is dynamic, weakly typed, and has first-class functions. However, like Java, JavaScript is heavily influenced by the C programming language. JavaScript also borrows many names and naming conventions from Java, but it does have very different semantics than Java.

JavaScript takes its key design principles from the Self and Scheme programming languages. It is a multi-paradigm language that supports object-oriented, imperative, and functional programming styles.

JavaScript was formalized in the ECMAScript language standard and was originally implemented as part of web browsers. It allowed client-side scripts to interact with the user, control the browser, communicate asynchronously, and alter the document content that was displayed. However, JavaScript is also used in applications outside of web pages, such as in PDF documents, site-specific browsers, and desktop widgets. Furthermore, newer and faster JavaScript VMs and frameworks have also increased the popularity of JavaScript for server-side web applications.

There are various similarities between Java and JavaScript, such as both have a C-like syntax. They are both object-oriented and typically sandboxed, especially when used inside a browser. Also, JavaScript was designed with Java's syntax and standard library in mind. All Java keywords were reserved in original JavaScript. JavaScript's standard library follows Java's naming conventions, and JavaScript's Math and Date objects are based on classes from Java 1.0. However, they are much more different than they are similar.

 While embedding JavaScript on a webpage, it may appear almost anywhere within the HTML file. However, the code is usually written either under the head tag or the body tag. Usually, the code written in the head will load before the code written in the body. This is mainly due to the order of the loading.

Usually, the code is placed in the head element. However, it is recommended that if the JavaScript is not required to be executed at the beginning of the page, it should be place at the bottom, in the body. This is due to the fact that the browser must go into single-threaded mode while the JavaScript loads and then executes. JavaScript at the top of the webpage causes the browser to pause while it deals with the JavaScript. If the JavaScript is placed at the bottom of the webpage, then browser can load the content on the page, which will be visible to the user. While, the user starts reading the content, the browser can then pause at leisure and deal with the JavaScript.

However, the actual placement of the JavaScript depends on individual webpage and the programmer. The placement will depend on when the programmer would require the JavaScript to load; in the beginning or later.

Image Courtesy: ajwebdesigner.in, goodellgroup.com

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Bloated SEO-centric article that doesn't answer the question.

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