code: function is(x: mixed, y: mixed): boolean {
    // SameValue algorithm
    if (x === y) { // Steps 1-5, 7-10
      // Steps 6.b-6.e: +0 != -0
      // Added the nonzero y check to make Flow happy, but it is redundant
      return x !== 0 || y !== 0 || 1 / x === 1 / y;
    } else {
      // Step 6.a: NaN == NaN
      return x !== x && y !== y;
    }
  }
docs: inlined Object.is polyfill to avoid requiring consumers ship their own
  https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is