Full Idea
Sartre defends a view of consciousness as nothing but a directedness towards objects, insisting that these objects are transcendent with respect to that consciousness; hence Sartre is one of the first genuine externalists.
Clarification
'Transcendent' means beyond, here; Externalists say mind is partly defined by external factors
Gist of Idea
Sartre says consciousness is just directedness towards external objects
Source
report of Jean-Paul Sartre (Being and Nothingness [1943]) by Mark Rowlands - Externalism Ch.1
Book Reference
Rowlands,Mark: 'Externalism' [Acumen 2003], p.4
A Reaction
An ancestor here is, I think, Schopenhauer (Idea 4166). The idea is attractive, as we are brought up with idea that we have a thing called 'consciousness', but if you removed its contents there would literally be nothing left.
Related Idea
Idea 4166 A consciousness without an object is no consciousness [Schopenhauer]