javascript and thymeleaf

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 th:each in Thymeleaf is primarily used for iterating over collections within HTML templates, not directly within JavaScript code. It processes on the server-side to generate HTML before the JavaScript executes in the browser. However, you can use th:each to generate JavaScript code dynamically based on data from your server. Here's how:

Generating JavaScript with th:each
  • Server-Side Iteration: Use th:each within a <script> tag to loop through a collection provided by your Spring Boot controller.
Code
    <script th:inline="javascript">        /*<![CDATA[*/        var items = [];        /*[# th:each="item : ${itemList}"]*/            items.push(/*[[${item}]]*/);        /*[/]*/        console.log(items);        /*]]>*/    </script>
  • th:inline="javascript": Enables Thymeleaf to process the script tag.
  • /*<![CDATA[*/ and /*]]>*/: Wraps the JavaScript code to prevent XML parsing errors, especially with older Thymeleaf versions.
  • /*[# th:each="item : ${itemList}"]*/: Starts a Thymeleaf loop over the itemList.
  • items.push(/*[[${item}]]*/);: Adds each item to the JavaScript items array. /*[[${item}]]*/ is an inline expression that will be replaced with the actual item value.
  • /*[/]*/: Closes the th:each loop.
  • Accessing Generated Data: Your JavaScript code can now use the items array populated by the server-side Thymeleaf processing.
Important Considerations
  • Server-Side vs. Client-Side:
    Thymeleaf processes th:each on the server, generating HTML and JavaScript. JavaScript then executes on the client's browser.
  • Data Types:
    Ensure that the data types being passed from the server are compatible with JavaScript.
  • Inline Expressions:
    Use /*[[${variable}]]*/ for inline expressions within JavaScript, as opposed to ${variable} which is used in HTML attributes.
  • CDATA:
    The CDATA section is crucial for older Thymeleaf versions to prevent parsing errors.
  • View Source:
    Inspect the generated HTML source in your browser to verify the JavaScript output.
Example
Controller (Java):
Java
import org.springframework.stereotype.Controller;import org.springframework.ui.Model;import org.springframework.web.bind.annotation.GetMapping;import java.util.Arrays;import java.util.List;@Controllerpublic class MyController {    @GetMapping("/example")    public String example(Model model) {        List<String> items = Arrays.asList("apple", "banana", "cherry");        model.addAttribute("itemList", items);        return "example";    }}
Template (HTML):
Code
<!DOCTYPE html><html xmlns:th="http://www.thymeleaf.org"><head>    <title>Thymeleaf Example</title></head><body>    <h1>Thymeleaf Example</h1>    <script th:inline="javascript">        /*<![CDATA[*/            var items = [];            /*[# th:each="item : ${itemList}"]*/                items.push(/*[[${item}]]*/);            /*[/]*/            console.log(items);        /*]]>*/    </script></body></html>
This example will output the following JavaScript in your browser's console:
JavaScript
var items = ["apple", "banana", "cherry"];console.log(items);
In summary, while th:each cannot be used directly inside JavaScript code, it can generate JavaScript code based on the data from the server, allowing you to dynamically create JavaScript arrays or other structures.

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