SyntaxError: Invalid left-hand side in assignment

[regseb]

function foo(a, b) {
  bar("" + a, b)
}

function bar(c, d) {
  return (c = d), d
}

Deobfuscate the above code (extracted from function n3(e) and i_(e,t,n) in this file) generates code with a syntax error:

function foo(a, b) {
  "" + a = b, b;
}