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--- java-script:hello-world [2023/08/08 22:21] – odefta
+++ java-script:hello-world [2023/08/08 23:12] (current) – odefta
@@ Line 3: / Line 3: @@
 The following script will display 'Hello World' both in a popup window and in the browser's console. To execute the script, it must be run within a web browser.
 <note>You can view the console output by accessing the browser's developer tools.</note>
+===== HTML + JS code in the same file =====
 <code javascript hello-world-js.html>
@@ Line 21: / Line 23: @@
 </html>
 </code>
+<note>
+The **document.querySelector** method is a very useful and commonly used function in JavaScript that returns the first element within the document that matches a specified selector or group of selectors. \\
+The syntax looks like this:
+<code javascript>
+const element = document.querySelector(selector);
+</code>
+Here, selector is a string containing one or more CSS selectors separated by commas. This method will return the first element that is a descendant of the document that matches the specified selectors. \\
+__Example 1__:
+<code javascript>
+<div id="container">
+  <p class="text">Hello, World!</p>
+</div>
+</code>
+You could use **document.querySelector** to select the <p> element with the class "text":
+<code javascript>
+const textElement = document.querySelector('.text');
+console.log(textElement.textContent); // Outputs "Hello, World!"
+</code>
+Or you could select it by its parent's ID:
+<code javascript>
+const textElement = document.querySelector('#container .text');
+</code>
+**#container .text** selector targets elements with the class text that are descendants of the element with the ID container. It doesn't matter how deeply nested the .text elements are within #container; they will be selected.
+__Example 2__:
+<code javascript>
+<div id="container" class="text">Hello World!</div>
+</code>
+To select the text 'Hello World':
+<code javascript>
+const textElement = document.querySelector('#container.text');
+</code>
+**#container.text** selector targets an element that has both the ID container and the class text. It's looking for a single element that matches both of these criteria.
+<note important>
+If you want to select elements with the class text that are inside an element with the ID container, use **#container .text**. \\ If you want to select an element that has both the ID container and the class text, use **#container.text**.
+</note>
+</note>
 <note>
@@ Line 52: / Line 99: @@
 </note>
+===== HTML + JS code in separated files =====
+HTML code:
+<code html hello-world.html>
+<!DOCTYPE html>
+<html lang="en">
+<head>
+    <meta charset="UTF-8">
+    <title>Hello World!</title>
+</head>
+<body>
+    <h1>Hello World! from an imported script file</h1>
+    <script src="./hello-script.js"></script>
+</body>
+</html>
+</code>
+Java Script code:
+<code javascript hello-script.js>
+alert('Hello world!');
+const h1 = document.querySelector('h1');
+console.log(h1.textContent);
+</code>
+<note tip>See also [[java-script:script-tag-placement|where to place the script tag]].</note>