Every time, the return value of callbackFn is passed into callbackFn again on next invocation as accumulator. It runs a 'reducer' callback function over all elements in the array, in ascending-index order, and accumulates them into a single value. The reduce() method is an iterative method. In this case, if the array is empty (so that there's no first value to return as accumulator), an error is thrown.

If initialValue is not specified, accumulator is initialized to the first value in the array, and callbackFn starts executing with the second value in the array as currentValue. If initialValue is specified, callbackFn starts executing with the first value in the array as currentValue. initialValue OptionalĪ value to which accumulator is initialized the first time the callback is called. On first call, 0 if initialValue was specified, otherwise 1. The index position of currentValue in the array. On first call, the value of array if an initialValue was specified, otherwise the value of array. On first call, initialValue if specified, otherwise the value of array. The value resulting from the previous call to callbackFn. The function is called with the following arguments: accumulator For the last invocation, the return value becomes the return value of reduce(). Its return value becomes the value of the accumulator parameter on the next invocation of callbackFn. ()Ī function to execute for each element in the array.Object.prototype._lookupSetter_() Deprecated.Object.prototype._lookupGetter_() Deprecated.Object.prototype._defineSetter_() Deprecated.

Object.prototype._defineGetter_() Deprecated.You can then iterate over each key in the object using forEach(). The Object.keys() function returns an array of the object's own enumerable

But you can iterate over a JavaScript object using forEach() if you transform the object into an array first, using Object.keys(), Object.values(), or Object.entries(). JavaScript's Array#forEach() function lets you iterate overīut not over an object.

Javascript for each element