HIGHER-ORDER FUNCTIONS
A higher-order function is a function that takes a function as an argument or returns a function. The higher-order function makes your code easier to understand and maintain. It also makes it easy to combine functions with each other. for examples .filter(), .map() and .reduce().Thesefunctions take a function as an argument. These are higher-order functions.
Filter
This method creates a new array with all elements that pass the test implemented by the provided function.
const words = ['spray', 'limit', 'elite', 'exuberant', 'destruction', 'present'];const result = words.filter(word => word.length > 6);console.log(result);// expected output: Array ["exuberant", "destruction", "present"]
Map
Let’s take the same list of people and an array of names that a person loves to watch movies. The map method creates a new array populated with the results of calling a provided function on every element in the calling array.
const movieLovers = [‘John Doe’, ‘Liam Smith’, ‘Jessy Pinkman’];const result = words.map(word => word.length > 6);console.log(result);
Reduce
This method used to reduce the array to a single value and executes a provided function for each value of the array (from left-to-right) and the return value of the function is stored in an accumulator.
const array1 = [1, 2, 3, 4];
const reducer = (accumulator, currentValue) => accumulator + currentValue;// 1 + 2 + 3 + 4
console.log(array1.reduce(reducer));
// expected output: 10// 5 + 1 + 2 + 3 + 4
console.log(array1.reduce(reducer, 5));
// expected output: 15
Parameter: This method accepts two parameters.
- Function(total, currentValue, index, arr): It is the required parameter and used to run for each element of the array. It contains four-parameter which are listed below:
- Total: It is the required parameter and used to specify the initialValue or the previously returned value of the function.
- CurrentValue: It is a required parameter and used to specify the value of the current element.
- CurrentIndex: It is an optional parameter and used to specify the array index of the current element.
- Arr: It is an optional parameter and used to specify the array object the current element belongs to.
- Initial value: It is an optional parameter and used to specify the value to be passed to the function as the initial value.
