Improper integral convergence

$\int_{-\infty }^{0} xe^x dx$

Hi. Online calculators are telling me this converges to -1. My first instinct is that it diverges to negative infinity but I get what looks like an indeterminate form when I work through this. Can someone please explain why this converges to negative one? Thanks for your time. 

here's what I have when after I substitute the bounds of the  integral:
-1 - [ ($-\infty $ -1) (1)]  


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