You need inject IJSRuntime for JS. It allows to load JavaScript code to your component.

If your JS function has a specific name, you can call with these function: InvokeAsync/InvokeVoidAsync.

Example:

Add script tag in your _Host.cshtml (P.S. ~ is equal to your wwwroot folder)

...
<script src="~/js/myJS.js"></script>
<script src="_framework/blazor.server.js"></script>

myJS.js

function MyScript(name) {
    return "Hello " + name;
}

Test.razor

@page "/test"
@inject IJSRuntime JS

<p id="myId">@Text</p>
<button @onclick="OnClick">Submit</button>

@code {
    private string Text { get; set; }

    private async void OnClick()
    {
        var exampleText = "World!";
        try
        {
            Text = await JS.InvokeAsync<string>("MyScript", exampleText);
        }
        catch(JSException ex)
        {
            Text = ex.Message;
        }

        StateHasChanged();
    }
}

Example after pushed the button:

If your JS script use a function onload (for example), you could override and use the OnAfterRenderAsync function.

    protected override async Task OnAfterRenderAsync(bool firstRender)
    {
        //invoke only one time, after your component is loaded
        if (firstRender)
        {
            await JS.InvokeVoidAsync("onload");
        }
        
    }

I don't know rapi-doc, maybe you could pass the json through backend with a variable.