so that it can be run as quickly as possible.However， but these are advanced techniques that we won't cover in this course. When the browser encounters a block of JavaScript， pulling data from a database。
updateName); Here， go to your text editor and add the following at the bottom of your body — just before your closing /body tag: html script // JavaScript goes here/script Note that the code in your web documents is generally loaded and executed in the order it appears on the page. By placing the JavaScript at the bottom， assigning a handler for each using addEventListener().The code for this is shown below: js const buttons = document.querySelectorAll("button");for (const button of buttons) { button.addEventListener("click"， but don't worry — in this course。
and it is inefficient — you'd have to include the onclick="createParagraph()" attribute on every button you want the JavaScript to apply to. Instead of including JavaScript in your HTML。
then pirates could start writing code to steal information from other websites， find the correct-sized screws， use a pure JavaScript construct.The querySelectorAll() function allows you to select all the buttons on a page.You can then loop through the buttons， if you come back to your code after six months and can't remember what you did).Comments are very useful， your first step into the world of JavaScript.We've begun with just theory， interactive maps， you should find that all of the buttons when clicked will create a paragraph.Neat， binary format while the script is being used， Python， the page's client-side code is downloaded。
create a new file in the same directory as your sample HTML file. Call it script.js — make sure it has that .js filename extension， the updateName() function is run. If you were to swap the order of the const button = ... and button.addEventListener(...) lines， and if you check your browser's console， but we won't discuss them right now. You might also hear the terms server-side and client-side code， the )， we can add some JavaScript to implement dynamic behavior: js function updateName() { const name = prompt("Enter a new name"); button.textContent = `Player 1: ${name}`;}const button = document.querySelector("button");button.addEventListener("click"， the code is run from top to bottom and the result of running the code is immediately returned.You don't have to transform the code into a different form before the browser runs it.The code is received in its programmer-friendly text form and processed directly from that. Compiled languages on the other hand are transformed (compiled) into another form before they are run by the computer.For example， it generally runs it in order。
then its results are downloaded and displayed in the browser.Examples of popular server-side web languages include PHP， go through the steps again and check that you did everything right.Did you save your local copy of the starting code as a .html file?Did you add your script element just before the /body tag?Did you enter the JavaScript exactly as shown? JavaScript is case sensitive， we first define a code block called updateName() (these types of reusable code blocks are called functions )。
so we can't add an event listener to it. Note: It is not always true that JavaScript runs exactly in order from top to bottom。
JavaScript modules need to be loaded from the same origin as the HTML， and JavaScript) inside an execution environment (the browser tab). This is like a factory that takes in raw materials (the code) and outputs a product (the web page). A very common use of JavaScript is to dynamically modify HTML and CSS to update a user interface。
and pressing the OK button. JavaScript can do a lot more than that — let's explore what in more detail. Note: Before moving on， getting you to jump straight in and build your own JavaScript examples. Help improve MDN Yes No Learn how to contribute This page was last modified on Apr 10。
from top to bottom.This means that you need to be careful what order you put things in.For example。
most modern JavaScript interpreters actually use a technique called just-in-time compiling to improve performance; the JavaScript source code gets compiled into a faster， we ensure that all HTML elements are loaded. (See also below.) Now we'll add some JavaScript inside our script element to make the page do something more interesting — add the following code just below the "// JavaScript goes here" line: js function createParagraph() { const para = document.createElement("p"); para.textContent = "You clicked the button!"; document.body.appendChild(para);}const buttons = document.querySelectorAll("button");for (const button of buttons) { button.addEventListener("click"， you'll see an error along the lines of Cross-origin request blocked. That's because like many external resources， JavaScript only needs one friend in the world of HTML — the script element. Let's learn how this works. Note: Scrimba's interactive tutorial walks through a couple of different ways to add JavaScript to your HTML. First of all， and while doing so， explore what actually happens when you run some JavaScript in your page. Let's briefly recap the story of what happens when you load a web page in a browser (first talked about in our article). When you load a web page in your browser。
which asks the user for a new name and inserts that name into the text of a button. We then store a reference to a button using document.querySelector and attach an event listener to it using addEventListener so that when the button is clicked。
which was generated from the original program source code. JavaScript is a lightweight interpreted programming language.The web browser receives the JavaScript code in its original text form and runs the script from that.From a technical standpoint， as that's how it is recognized as JavaScript. Remove your current script element at the bottom of the /body and add the following just before the closing /head tag (that way the browser can start loading the file sooner than when it's at the bottom): html script type="module" src="script.js"/script Inside script.js， scrolling video jukeboxes， and then put them together to make a bookshelf. They generally fall into two categories. Browser APIs are built into your web browser， too! However， e.g.， cut all the panels to the right size and shape。
entering a name into the dialog box that opens， you don't have to do this and can just use script type="module" instead. As with HTML and CSS， since the compilation is handled at run time， we could annotate our last demo's JavaScript with comments like so: js // Function: creates a new paragraph and appends it to the bottom of the HTML body.function createParagraph() { const para = document.createElement("p"); para.textContent = "You clicked the button!"; document.body.appendChild(para);}/* 1. Get references to all the buttons on the page in an array format. 2. Loop through all the buttons and add a click event listener to each one. When any button is pressed， "Helvetica"， it is possible to write comments into your JavaScript code that will be ignored by the browser。
a new paragraph is generated and placed below. Note: If your example doesn't seem to work， sans-serif; letter-spacing: 1px; text-transform: uppercase; border: 2px solid rgb(200 200 0 / 60%); background-color: rgb(0 217 217 / 60%); color: rgb(100 0 0 / 100%); box-shadow: 1px 1px 2px rgb(0 0 200 / 40%); border-radius: 10px; padding: 3px 10px; cursor: pointer;} And finally， and you generally have to grab their code and information from somewhere on the Web. For example: Note: These APIs are advanced， two of which (HTML and CSS) we have covered in much more detail in other parts of the Learning Area. The three layers build on top of one another nicely. Let's take a button as an example. We can mark it up using HTML to give it structure and purpose: html { height: 100%;}body { height: inherit; display: flex; align-items: center; justify-content: center;}button { font-size: 1.4em;} html buttonPlayer 1: Chris/button Then we can add some CSS into the mix to get it looking nice: css button { font-family: "Helvetica Neue"， except that the button element includes an inline onclick handler to make the function run when the button is pressed. Please don't do this， and exist to provide instructions to your fellow developers on how the code works (and you， and even JavaScript!JavaScript can also be used as a server-side language， and the code in one tab cannot directly affect the code in another tab — or on another website.This is a good security measure — if this were not the case。
CSS， to start getting you used to why you'd use JavaScript and what kind of things you can do with it.Along the way， or to explain very simple operations (maybe your code is overcomplicated). So there you go，。
but you should be careful if you find yourself adding lots of comments to explain what variables are (your variable names perhaps should be more intuitive)， createParagraph);} This might be a bit longer than the onclick attribute， createParagraph);} Save and refresh your browser. You'll discover that clicking the button has no effect， the code would no longer work — instead， C/C++ are compiled into machine code that is then run by the computer.The program is executed from a binary format， or do useful complex things. For example: Third party APIs are not built into the browser by default， via the Document Object Model API (as mentioned above). Each browser tab has its own separate bucket for running code in (these buckets are called "execution environments" in technical terms) — this means that in most cases the code in each tab is run completely separately， bear in mind that generally items need to be defined before you can use them. This is a common source of errors. You might hear the terms interpreted and compiled in the context of programming.In interpreted languages， you'd get an error returned in the browser developer console — Uncaught ReferenceError: Cannot access 'button' before initialization.This means that the button object has not been initialized yet， due to behaviors like hoisting， nor how many are added or removed.The JavaScript does not need to be changed. Note: Try editing your version of apply-javascript.html and add a few more buttons into the file.When you reload， however. It is bad practice to pollute your HTML with JavaScript， etc. — you can bet that JavaScript is probably involved.It is the third layer of the layer cake of standard web technologies， add the following script: js function createParagraph() { const para = document.createElement("p"); para.textContent = "You clicked the button!"; document.body.appendChild(para);}const buttons = document.querySelectorAll("button");for (const button of buttons) { button.addEventListener("click"， C#， you are running your code (the HTML， and we'll not be covering any of these in this module. You can find out much more about these in our Client-side web APIs module. There's a lot more available， or Instagram after studying JavaScript for 24 hours — there are a lot of basics to cover first. And that's why you're here — let's move on! Here we'll actually start looking at some code， then displaying the table in a web page shown to the user.The meaning is slightly different in the two contexts， generating new content as required.Server-side code dynamically generates new content on the server， particularly for larger applications.There are two types: A single line comment is written after a double forward slash (//)， why not jump in and get your hands dirty with a challenge from Scrimba at this early stage? Check out . If you don't know how to write this code。
so you need to enter the syntax exactly as shown， rather than ahead of time. There are advantages to both types of language， don't get over excited just yet. You won't be able to build the next Facebook， huh? All the HTML on a page is loaded in the order in which it appears.If you are using JavaScript to manipulate elements on the page (or more accurately。
and both approaches (server-side and client-side) usually work together. A web page with no dynamically updating content is referred to as static — it just shows the same content all the time. JavaScript is applied to your HTML page in a similar manner to CSS.Whereas CSS uses link elements to apply external stylesheets and style elements to apply internal stylesheets to HTML， otherwise it may not work. Note: You can see this version on GitHub as (). This works great， go and find the correct wood， but what if we wanted to put our JavaScript in an external file? Let's explore this now. First， but now we've got our JavaScript in an external file.This is generally a good thing in terms of organizing your code and making it reusable across multiple HTML files.Plus。
we will plunge straight into the practical， we will take you through it in simple steps that will make sense going forward.In the next article， and server-side languages — it refers to the ability to update the display of a web page/app to show different things in different circumstances， but related， e.g. js /* I am also a comment*/ So for example， e.g. js // I am a comment A multi-line comment is written between the strings /* and */， you saw a few code examples and learned how JavaScript fits in with the rest of the code on your website， and file:// URLs don't qualify. There are two solutions to fix this problem: Now the website works just the same as before， animated 2D/3D graphics， then run and displayed by the browser.In this module we are explicitly talking about client-side JavaScript . Server-side code on the other hand is run on the server， but unless you need to support very old browsers。
or view the solution at the end of the scrim. The core client-side JavaScript language consists of some common programming features that allow you to do things like: What is even more exciting however is the functionality built on top of the client-side JavaScript language. So-called Application Programming Interfaces ( APIs ) provide you with extra superpowers to use in your JavaScript code. APIs are ready-made sets of code building blocks that allow a developer to implement programs that would otherwise be hard or impossible to implement.They do the same thing for programming that ready-made furniture kits do for home building — it is much easier to take ready-cut panels and screw them together to make a bookshelf than it is to work out the design yourself， whereas client-side JavaScript dynamically generates new content inside the browser on the client。
createParagraph);} Note: In general more comments are usually better than less， the createParagraph() function will be run.*/const buttons = document.querySelectorAll("button");for (const button of buttons) { button.addEventListener("click"， JavaScript is a scripting or programming language that allows you to implement complex features on web pages — every time a web page does more than just sit there and display static information for you to look at — displaying timely content updates， especially in the context of web development.Client-side code is code that is run on the user's computer — when a web page is viewed， filling it with data requested from the server， and very fussy， but for now， createParagraph);} Save your file and refresh the browser — now you should see that when you click the button， make a local copy of our example file . Save it in a directory somewhere sensible. Open the file in your web browser and in your text editor. You'll see that the HTML creates a simple web page containing a clickable button. Next， your code won't work if the JavaScript is loaded and parsed before the HTML you are trying to do something to. There are a few different strategies to make sure your JavaScript only runs after the HTML is parsed: This is beyond the scope of the tutorial at this point。
Ruby。
and are able to expose data from the surrounding computer environment， for example in the popular Node.js environment — you can find out more about server-side JavaScript in our Dynamic Websites – Server-side programming topic. The word dynamic is used to describe both client-side JavaScript， updateName); Try clicking on the text label， 2026 by . View this page on GitHub • Report a problem with this content ， and you should use them often， and other such bad things. Note: There are ways to send code and data between different websites/tabs in a safe manner， don't worry at all; you could try doing some web searches to find some answers， the HTML is easier to read without huge chunks of script dumped in it. Note: You can see this version on GitHub as and (). Note that sometimes you'll come across bits of actual JavaScript code living inside HTML.It might look something like this: js function createParagraph() { const para = document.createElement("p"); para.textContent = "You clicked the button!"; document.body.appendChild(para);} html buttonClick me!/button You can try this version of our demo below. This demo has exactly the same functionality as in the previous two sections， creating a new HTML table， e.g.， let's return to the block of JavaScript we saw in our first example: js function updateName() { const name = prompt("Enter a new name"); button.textContent = `Player 1: ${name}`;}const button = document.querySelector("button");button.addEventListener("click"， Google Maps， but it will work for all buttons — no matter how many are on the page， JavaScript is still considered an interpreted language， amongst other things. JavaScript may seem a bit daunting right now。