Voice of a Developer: JavaScript Array Methods

var numbers = [1, 2, 3, 4];
var ary1 = numbers.map(function(item, index) {
return item * 2;
});
console.log(ary1); // [2, 4, 6, 8]

Therefore, the above code leverages Map method & iterates over each item and produces a new Array containing product by 2. The index is optional to pass & you could use inside callback function (item, index)

Reduce

The reduce() method reduces the array to a single value.

Parameters

A callback function runs on each value and takes four arguments:

previousValue- value returned previously
currentValue- current element being processed
index- index of the current Array element
array- array map was called upon

Example

var numbers = [1,2,3,4];
var total=numbers.reduce (function (prev,current) {
return prev+current;
});
console.log(total); // 10

Look at stack trace where prev & current values could be debugged. This method processes two values at a time.

Filter

It creates a new array with all elements which pass the test.

Parameters

Callback- to test each element of the array. It returns true to keep the element, false otherwise.

var numbers = [1,2,3,4];
var ary1 = numbers.filter (function (value) {
return value > 2;
});
console.log (ary1); // [3,4]

Find

It returns a value in the array if it’s found, otherwise undefined is returned.

Parameters

Callback- to test each element of array.

element- current processed value.
index- index of current Array element.
array- array map was called upon.
1. var numbers = [1,2,3,4];
2. var value = numbers.find (function (element) {
3. return element == 2;
4. });
5. console.log(value); // 2

Every

The purpose of this method is to iterate over each element of an Array and validate for all elements. Here is the syntax from VSCode.

Example

function isPrime(number) {
var start = 2;
while(start <= Math.sqrt(number)) {
if(number % start++ < 1) return false;
}
return number > 1;
}
var numbers = [3, 5, 7];
var flag = numbers.every(isPrime);
console.log(flag); // returns true

Summary

Please use these methods as it simplifies your code and reduces your time in these operations.

Voice of a Developer: JavaScript Array Methods - Part Seventeen

Introduction

Map

Reduce

Filter

Find

Every

Summary