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The difference between the two functions is simple. The two arguments that these functions require are the accumulated value and the element of the collection. The fold() and reduce() functions can be used to apply operations sequentially on a collection of elements and return the accumulated result. To be more specific, we can use the sumOf() extension function with Int, Long, Double, UInt, ULong, BigInteger, and BigDecimal data types. So, there’s no need to have functions with different names for each data type, just like sumBy() and sumByDouble(). Despite that, we can also use this function with a list of Byte, Short, Long, and Float elements: val sumBy = numbers.sumBy )Īs shown above, we can use the same function to sum Int and UInt values and return Int and UInt summations, respectively. This function always returns an integer value. Here is an example that uses the for.We can use the sumBy() function to find the sum of all values that are mapped by applying the selector function to each element in the collection. This method works in all modern and old browsers including Internet Explorer 6 and higher. The most straightforward way to loop through an object's properties is by using the for.in statement. Methods to loop through objects using javascript for.in Loop Map() will give you TypeError: items.map is not a function: items.map(item => If you have an array that is considered to be an object in javascript, you can’t loop through the array using map(), forEach(), or a for.of loop.

Introduction to looping through objects using javascript