Using "preLaunchTasks" and Naming a Task in Visual Studio Code

So, if it's still relevant, or if someone finds this thread with the same problem, I've just figured it out how it works:

In the tasks.json, you need to create a 'tasks' array - code hint will help you with that - which holds an array of objects. Inside an object, you can have the 'taskName' key-value pair.

Example:

{
    "version": "0.1.0",
    "command": "npm",
    "isShellCommand": true,
    "args": ["run-script", "webpack"],
    "showOutput": "always",
    "tasks": [
        { 
            "taskName": "runwebpack",
            "suppressTaskName": true
        }
    ]
}

In my case, I had to run the npm run-script webpack command before running my project. In the launch.json file, the "preLaunchTask": "runwebpack" will work now.

Note: the suppressTaskName is true in my example. Omitting it, or setting it to false will result in VS Code appending the taskName after the command.

A more general approach would be something like this:

{
    "version": "0.1.0",
    "command": "npm",
    "isShellCommand": true,
    "args": ["run-script"],
    "showOutput": "always",
    "tasks": [
        { "taskName": "webpack" }
    ]
}

With the latter example, you can extend the tasks array with other scripts to be run also.

Hint for my usage: npm run-script fetches what to do from the package.json file's scripts object.

Edit: this works with VS Code 1.3.1

FWIW, I'm using VS Code 1.20.1 and here's how I got my preLaunchTask to work:

In launch.json:

{
  "version": "0.2.0",
  "configurations": [
    {
        "type": "node",
        "request": "launch",
        ...
        "preLaunchTask": "npm: build",
    }
  ]
}

In my package.json:

{
  ...
  "scripts": {
     "build": "tsc"
     ...
  }
}