Interaction in JS buffers

Indium comes with a minor mode called indium-interaction-mode for interactive programming. To enable it in all JavaScript buffers, add something like the following to your Emacs configuration:

(require 'indium)
(add-hook 'js-mode-hook #'indium-interaction-mode)

When indium-interaction-mode is on, you can evaluate code, inspect objects and add or remove breakpoints from your buffers.

Evaluating and inspecting

Here’s a list of available keybindings:

  • C-x C-e: Evaluate the JavaScript expression preceding the point.
  • C-M-x: Evaluate the innermost function enclosing the point.
  • C-c M-i: Inspect the result of the evaluation of an expression (see The inspector).
  • C-c M-:: Prompt for an expression to evaluate and inspect.
  • M-x indium-eval-buffer: Evaluate the entire buffer.
  • M-x indium-eval-region: Evaluate the current region.

Switching to the REPL buffer

Press C-c C-z from any buffer with indium-interaction-mode turned on to switch back to the REPL buffer (see The REPL).

Adding and removing breakpoints

You need to first make sure that Indium is set up correctly to use local files (see General configuration).

  • C-c b b: Add a breakpoint
  • C-c b c: Add a conditional breakpoint
  • C-c b k: Remove a breakpoint
  • C-c b t: Toggle a breakpoint
  • C-c b K: Remove all breakpoints from the current buffer
  • C-c b e: Edit condition of a breakpoint
  • C-c b l: List all breakpoints and easily jump to any breakpoint
  • C-c b d: Deactivate all breakpoints (the runtime won’t pause when hitting a breakpoint)
  • C-c b a: Activate all breakpoints (it has no effect if breakpoints have not been deactivated)

The left fringe or margin can also be clicked to add or remove breakpoints.

Once a breakpoint is set, execution will stop when a breakpoint is hit, and the Indium debugger pops up (see The stepping debugger).

Since Indium 0.7, breakpoints are supported in source files with an associated sourcemap, see Using sourcemaps.


Breakpoints are persistent: if the connection is closed, when a new connection is made Indium will attempt to add back all breakpoints.