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# Runtime errors
There are several runtime errors that Gleam code can throw. This documentation
lists them and their runtime properties.
On Erlang runtime errors are Erlang maps thrown with `erlang:error/1`, having at
least these properties:
| Key | Type | Value |
| --- | ---- | ----- |
| gleam_error | Atom | See individual errors |
| message | String | See individual errors |
| module | String | The module the error occured in |
| function | String | The function the error occured in |
| line | Int | The line number the error occured on |
On JavaScript runtime errors are instances of the JavaScript `Error` class,
having at least these properties added to them:
| Key | Type | Value |
| --- | ---- | ----- |
| gleam_error | String | See individual errors |
| message | String | See individual errors |
| module | String | The module the error occured in |
| function | String | The function the error occured in |
| line | Number | The line number the error occured on |
## Todo
A panic that indicates that the code has not yet been completed, intended for
use in development.
```gleam
todo
todo as "some message"
```
| Key | Erlang Value | JavaScript Value |
| --- | ------------ | ---------------- |
| gleam_error | `todo` | `"todo"` |
| message | The given message | The given message |
## Panic
An explicit panic to unconditionally error.
```gleam
panic
panic as "some message"
```
| Key | Erlang Value | JavaScript Value |
| --- | ------------ | ---------------- |
| gleam_error | `panic` | `"panic"` |
| message | The given message | The given message |
## Let assert
An inexhaustive pattern match, erroring if the pattern does not match.
```gleam
let assert Ok(x) = something()
```
| Key | Erlang Value | JavaScript Value |
| --- | ------------ | ---------------- |
| gleam_error | `let_assert` | `"let_assert"` |
| message | The given message | The given message |
| value | The unmatched value | The unmatched value |