code: function hasPrecedence(op1, op2) {
      invariant(PRECEDENCE[op1] && PRECEDENCE[op2], `Missing precedence number for
              ${JSON.stringify(op1)} or ${JSON.stringify(op2)}.
              See ${JSON.stringify(PRECEDENCE)}`);
  
      return PRECEDENCE[op1] < PRECEDENCE[op2];
  }
docs: Return true if the first operator has precedence over the second
  hasPrecedence('/', '+') => true
  
  @param {String} op1
  @param {String} op2