Show whitespace characters in Visual Studio Code

VS Code 1.6.0 and Greater

As mentioned by aloisdg below, editor.renderWhitespace is now an enum taking either none, boundary or all. To view all whitespaces:

"editor.renderWhitespace": "all", 

Before VS Code 1.6.0

Before 1.6.0, you had to set editor.renderWhitespace to true:

"editor.renderWhitespace": true

It can also be done via the main menu View -> Render Whitespace

Show whitespace characters in Visual Studio Code

change the settings.json, by adding the following codes!

the file path is .vscode/settings.json in your project root folder.

    // Place your settings in this file to overwrite default and user settings.
    {
        "editor.renderWhitespace": "all"
    }

just like this!
(PS: there is no "true" option!, even it also works.)

UPDATE (June 2019)

For those willing to toggle whitespace characters using a keyboard shortcut, you can easily add a keybinding for that.

In the latest versions of Visual Studio Code there is now a user-friendly graphical interface (i.e. no need to type JSON data etc) for viewing and editing all the available keyboard shortcuts. It is still under

File > Preferences > Keyboard Shortcuts (or use Ctrl+K Ctrl+S)

There is also a search field to help quickly find (and filter) the desired keybindings. So now both adding new and editing the existing keybindings is much easier:

Toggling whitespace characters has no default keybinding so feel free to add one. Just press the + sign on the left side of the related line (or press Enter, or double click anywhere on that line) and enter the desired combination in the pop-up window.

And if the keybinding you have chosen is already used for some other action(s) there will be a convenient warning which you can click and observe what action(s) already use your chosen keybinding:

As you can see, everything is very intuitive and convenient.
Good job, Microsoft!

---

Original (old) answer

For those willing to toggle whitespace characters using a keyboard shortcut, you can add a custom binding to the keybindings.json file (File > Preferences > Keyboard Shortcuts).

Example:

// Place your key bindings in this file to overwrite the defaults
[
    {
        "key": "ctrl+shift+i",
        "command": "editor.action.toggleRenderWhitespace"
    }
]

Here I have assigned a combination of Ctrl+Shift+i to toggle invisible characters, you may of course choose another combination.