From Batman News:
Last night a TV Critic for The New Yorker, Emily Nussbaum, tweeted out the lyrics to the song “Everybody Knows” by Leonard Cohen. The song appears in the opening title montage for Justice League and is performed by Sigrid, and it turns out it was Joss Whedon who decided to use it there.
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(I stuck it in JL too)
— Joss Whedon (@joss) December 4, 2017