node_modules/jszip/node_modules/core-js/library/modules/_to-primitive.js

// 7.1.1 ToPrimitive(input [, PreferredType])
var isObject = require('./_is-object');
// instead of the ES6 spec version, we didn't implement @@toPrimitive case
// and the second argument - flag - preferred type is a string
module.exports = function(it, S){
  if(!isObject(it))return it;
  var fn, val;
  if(S && typeof (fn = it.toString) == 'function' && !isObject(val = fn.call(it)))return val;
  if(typeof (fn = it.valueOf) == 'function' && !isObject(val = fn.call(it)))return val;
  if(!S && typeof (fn = it.toString) == 'function' && !isObject(val = fn.call(it)))return val;
  throw TypeError("Can't convert object to primitive value");
};