Studying all day long)
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var aCallable = require('../internals/a-callable');
var toObject = require('../internals/to-object');
var IndexedObject = require('../internals/indexed-object');
var lengthOfArrayLike = require('../internals/length-of-array-like');
var $TypeError = TypeError;
// `Array.prototype.{ reduce, reduceRight }` methods implementation
var createMethod = function (IS_RIGHT) {
return function (that, callbackfn, argumentsLength, memo) {
aCallable(callbackfn);
var O = toObject(that);
var self = IndexedObject(O);
var length = lengthOfArrayLike(O);
var index = IS_RIGHT ? length - 1 : 0;
var i = IS_RIGHT ? -1 : 1;
if (argumentsLength < 2) while (true) {
if (index in self) {
memo = self[index];
index += i;
break;
}
index += i;
if (IS_RIGHT ? index < 0 : length <= index) {
throw $TypeError('Reduce of empty array with no initial value');
}
}
for (;IS_RIGHT ? index >= 0 : length > index; index += i) if (index in self) {
memo = callbackfn(memo, self[index], index, O);
}
return memo;
};
};
module.exports = {
// `Array.prototype.reduce` method
// https://tc39.es/ecma262/#sec-array.prototype.reduce
left: createMethod(false),
// `Array.prototype.reduceRight` method
// https://tc39.es/ecma262/#sec-array.prototype.reduceright
right: createMethod(true)
};