Unable to unset / delete runtime bindings

[raidancampbell]

The Otto runtime exposes a Set function for setting a variable, but no equivalent deletion is available. The closest I could come to was another Set to otto.UndefinedValue(), but that doesn't yield the same behavior. The below code snippet describes what I'm trying to achieve.

func TestOtto(t *testing.T) {
	runtime := otto.New()

	_, err := runtime.Run("console.log(foo)")
	assert.NotNil(t, err)
	assert.Contains(t, err.Error(), "ReferenceError: 'foo' is not defined")

	err = runtime.Set("foo", "bar")
	assert.Nil(t, err)
	_, err = runtime.Run("console.log(foo)")
	assert.Nil(t, err)

	err = runtime.Set("foo", otto.UndefinedValue())
	assert.Nil(t, err)
	_, err = runtime.Run("console.log(foo)")
	assert.NotNil(t, err) // fails, err is nil
	assert.Equal(t, err, "ReferenceError: 'foo' is not defined") // fails, err is nil
}

[stevenh]

Happy to accept a PR to add this.