How could I call a Javascript function within the view of my ASP MVC application?

Question

How could I call a Javascript function within the view of my ASP MVC application?

Assign the href value to the anchor tag inside the C# foreach loop. The value will be retrieved from the Javascript function. How can we achieve this functionality in C# the MVC model?

It should get values from the javascript function without any event occurring.

.CSHTML file

@foreach (var item in Model.items)
{
    <a href="JavascriptFunction(item.tostring())" class="solutions-grid__card">
        Title
    </a>
}

Javascript function

function JavascriptFunction(str) {
    alert(str);
    return str.replace(/(?:^\w|[A-Z]|\b\w)/g, (word, index) => {
        return index === 0 ? word.toLowerCase() : word.toUpperCase();
    }).replace(/\s+/g, '');
}

The href tag value should have a Javascript returned value.

Answer 1

Instead of using a href, just use an onclick

<a onclick="JavascriptFunction(item.tostring())" class="solutions-grid__card">
    Title
</a>

Answer 2

To call a JavaScript function within the view of an ASP.NET MVC application, you can use the following approach:

Define the JavaScript function in a script tag in the View:

<script>
    function JavascriptFunction(str) {
        alert(str);
        return str.replace(/(?:^\w|[A-Z]|\b\w)/g, (word, index) => {
            return index === 0 ? word.toLowerCase() : word.toUpperCase();
        }).replace(/\s+/g, '');
    }
</script>

Inside the foreach loop in the View, use the Url.Action() method to generate the URL for the action method that will handle the request:

@foreach (var item in Model.items)
{
    <a href="@Url.Action("ActionMethodName", "ControllerName", new { str = item.ToString() })" class="solutions-grid__card">
        Title
    </a>
}

Here, ActionMethodName and ControllerName should be replaced with the name of the action method and controller, respectively.

In the Controller action method, retrieve the value of the str parameter and pass it to the JavaScript function:

public ActionResult ActionMethodName(string str)
{
    ViewBag.JavascriptResult = "<script>var result = JavascriptFunction('" + str + "');</script>";
    return View();
}

Here, ViewBag.JavascriptResult is used to store the result of the JavaScript function, which will be rendered in the View.

In the View, render the JavaScript result using the Html.Raw() method:

@Html.Raw(ViewBag.JavascriptResult)

This will execute the JavaScript function and store the result in the result variable. You can use this variable to set the value of the href tag dynamically.

<a href="http://example.com/@result" class="solutions-grid__card">
    Title
</a>

I hope this was helpful :)

Answer 3

You've stated your main criteria:

Assign the href value to the anchor tag inside the C# foreach loop.

Inside the loop, the Razor engine is executing in a C# context. The engine cannot switch to parsing/executing a JavaScript function. JavaScript is not executed by the Razor engine on the server.

Hence, your code will need to execute a C# function while in the foreach loop to provide the same output as the JavaScript function. Your JS function, JavascriptFunction is converting a string of words into a camel case string.

console.log(JavascriptFunction("This is some text"));
-> Output: "thisIsSomeText"

The C# equivalent is in the following Razor page (.cshtml). Reference links are added in the comments. See this link from Microsoft's documenation and this SO link post for calling a C# function from within the foreach loop.

Putting the C# function in a static class versus directly in a Razor page is better.

@page
@{
    string[] stringList = new string[]
    {
        "This is some text", // -> "thisIsSomeText"
        "Custom web component", // -> "customWebComponent"
        "Add to source control" // -> "addToSourceControl"
    };
}
<div style="display: grid;">
    @foreach (string item in stringList)
    {
        <a href="@ConvertToCamelCase(item)" class="solutions-grid__card">
            @item
        </a>
    }
</div>

@* https://stackoverflow.com/questions/5159877/how-do-i-define-a-method-in-razor
    https://learn.microsoft.com/en-us/aspnet/core/mvc/views/razor?view=aspnetcore-7.0#functions *@

@functions {
    // The method 'ConvertToCamelCase()' produces the equivalent
    // output as the JavaScript function in the '<script>' tag.
    public string ConvertToCamelCase(string str)
    {
        System.Text.RegularExpressions.Regex rx =
            new System.Text.RegularExpressions.Regex(@"(?:^\w|[A-Z]|\b\w)");

        // Convert first letter in each word
        // https://stackoverflow.com/questions/44567538/how-i-replace-a-text-like-javascript-in-c-sharp
        int index = 0;
        string result = rx.Replace(str, (System.Text.RegularExpressions.Match m) =>
        {
            // Increment 'index' AFTER it's been evaluated
            return index++ == 0 ? m.ToString().ToLower() : m.ToString().ToUpper();
        });
        // Remove all whitespaces
        // https://stackoverflow.com/questions/6219454/efficient-way-to-remove-all-whitespace-from-string
        return System.Text.RegularExpressions.Regex.Replace(result, @"\s+", "");
    }
}