Typescript – Why is –isolatedModules error fixed by any import

typescript

In a create-react-app typescript project, I tried to write this just to test some stuff quickly:

// experiment.test.ts
it('experiment', () => {
  console.log('test');
});

But it gives me the following error, with a red squiggly beneath it:

All files must be modules when the '–isolatedModules' flag is provided.

However, if I change the file to the following, then everything apparently is fine (except for the unused import of course):

// experiment.test.ts
import { Component} from 'react'; // literally anything, don't even have to use it

it('test', () => {
  console.log('test');
});

Why? What is happening here? What does --isolatedModules actually mean/do?

Best Answer

Typescript treats files without import/exports as legacy script files. As such files are not modules and any definitions they have get merged in the global namespace. isolatedModules forbids such files.

Adding any import or export to a file makes it a module and the error disappears.

Also export {} is a handy way to make a file a module without importing anything.

Related Solutions

Asp – GridView Create Fields Dynamically

You have to create a template class that implements ITemplate. See this example from MSDN. The code below extends my answer to this question to add a template column that displays Title|Author.

Markup:

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false" 
    OnRowCommand="GridView1_RowCommand" 
    OnRowEditing="GridView1_RowEditing"/>

Code:

protected void Page_Load(object sender, EventArgs e)
{
    BindGridView();
}

private DataTable GetBooksDataTable()
{
    var dt = new DataTable();
    dt.Columns.Add("ID", typeof(int));
    dt.Columns.Add("Title", typeof(string));
    dt.Columns.Add("Author", typeof(string));

    for (int index = 0; index < 10; index++)
    {
        dt.Rows.Add(index, "Title" + index, "Author" + index);
    }
    return dt;
}

private void BindGridView()
{
    var dt = GetBooksDataTable();

    GridView1.Columns.Clear();
    GridView1.ShowFooter = true;

    var cf = new CommandField();
    cf.HeaderText = "Action";
    cf.ShowEditButton = true;
    GridView1.Columns.Add(cf);

    for (int index = 0; index < dt.Columns.Count; index++)
    {
        var boundField = new BoundField();
        boundField.DataField = dt.Columns[index].ColumnName;
        boundField.HeaderText = dt.Columns[index].ColumnName;
        GridView1.Columns.Add(boundField);
    }

    CreateCustomTemplateField(GridView1, "Title|Author");

    GridView1.DataSource = dt;
    GridView1.DataBind();

    var footer = GridView1.FooterRow;
    var b = new LinkButton();
    b.Text = "Add New";
    b.CommandName = "Add New";
    footer.Cells[0].Controls.Add(b);
    for (int index = 1; index < dt.Columns.Count + 1; index++)
    {
        var tb = new TextBox();
        footer.Cells[index].Controls.Add(tb);
    }

}

private void CreateCustomTemplateField(GridView gv, string headerText)
{
    var customField = new TemplateField();
    customField.HeaderTemplate = new CustomTemplate(DataControlRowType.Header, headerText);
    customField.ItemTemplate = new CustomTemplate(DataControlRowType.DataRow, headerText);
    gv.Columns.Add(customField);
}

public class CustomTemplate : ITemplate
{
    private DataControlRowType _rowType;
    private string _headerText;

    public CustomTemplate(DataControlRowType rowType, string headerText)
    {
        _rowType = rowType;
        _headerText = headerText;
    }

    public void InstantiateIn(Control container)
    {
        switch (_rowType)
        {
            case DataControlRowType.Header:
                var header = new Literal();
                header.Text = _headerText;
                container.Controls.Add(header);
                break;
            case DataControlRowType.DataRow:
                var data = new Literal();
                data.DataBinding += DataRowLiteral_DataBinding;
                container.Controls.Add(data);
                break;
        }
    }

    private void DataRowLiteral_DataBinding(object sender, EventArgs e)
    {
        var data = (Literal)sender;
        var row = (GridViewRow)data.NamingContainer;
        data.Text = DataBinder.Eval(row.DataItem, "Title") + "|" + DataBinder.Eval(row.DataItem, "Author");
    }
}

protected void GridView1_RowCommand(object sender, GridViewCommandEventArgs e)
{
    Literal1.Text = e.CommandName;
}

protected void GridView1_RowEditing(object sender, GridViewEditEventArgs e)
{
    Literal1.Text = "Editing row index " + e.NewEditIndex.ToString();
}

R – Singleton Pattern in .Net is not possible

Just because it is possible to deliberately circumvent a pattern in this way does not mean that the pattern itself is "not possible".

Best Answer

Related Solutions

Asp – GridView Create Fields Dynamically

R – Singleton Pattern in .Net is not possible

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