Finding Your Way With .Map()

#webdev #programming #javascript #map

The map method allows us to transform each element of an array, without affecting the original array. It’s considered a higher-order function and a functional programming technique because it takes a function as an argument and we are performing computation without mutating the state of our application.

Map is a property that is inherited from the array prototype. Prototypes provide built-in-methods that objects come with (arrays are special types of objects in the eyes of JavaScript). While map may be a little more foreign, this prototype is no different than, for example, the Array.length prototype. These are simply methods that are baked into JavaScript. Array prototypes can be added and mutated by: Array.prototype. = ...

So what does .map() do?

Let’s say you have an array of temperatures in Celsius that you want to convert to Fahrenheit.

There are several ways to solve this problem. One way may be to write a for loop to create an array of Fahrenheit temperatures from the given Celsius temperatures.

With the for loop we might write:

const celciusTemps = [22, 36, 71, 54];
const getFahrenheitTemps = (function(temp) {
const fahrenheitTemps = [];
for (let i = 0; i < celciusTemps.length; i += 1) {
temp = celciusTemps[i] * (9/5) + 32
fahrenheitTemps.push(temp);
}
console.log(fahrenheitTemps); [71.6, 96.8, 159.8, 129.2
})();

**So how does a map work?

**
Map takes a function and applies that function to each element in the array. We could write a map a bit more verbose with ES5 to see this a bit more clearly.

const fahrenheitTemps = celciusTemps

   .map(function(elementOfArray) {
      return elementOfArray * (9/5) + 32;
   });
console.log(fahrenheitTemps); // [71.6, 96.8, 159.8, 129.2]

Example

const people = [
   {name: Steve, age: 32},
   {name: Mary, age: 28},
   {name: Bill, age: 41},
];
const getNames = (function(person) {
   const names = [];
   for (let i = 0; i < people.length; i += 1) {
      name = people[i].name;
      names.push(name);
   }
   console.log(names); // [Steve, Mary, Bill];
})();
With map:

const names = people.map(e => e.name);
console.log(names) // [Steve, Mary, Bill];

if you want to learn more deeply, reference this URL
https://www.freecodecamp.org/news/finding-your-way-with-map-aecb8ca038f6

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