add js doc b00tc4mp#14

staff/david-alonso/playground/javascript/README.md

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+# javascript
+
+![js logo](https://upload.wikimedia.org/wikipedia/commons/thumb/6/6a/JavaScript-logo.png/600px-JavaScript-logo.png)
+
+## Saludo
+```sh
+console.log("¡Hola, mundo!");
+```
+## Suma
+```sh
+const suma = 10 + 15 
+```
+## Multiplicar
+```sh
+var numbers = [2, 4, 6, 8]
+
+function multipyByTwo (numbers) {
+    var result = numbers.map(function(number) {
+        return number * 2
+    })
+    return result
+}
+
+multipyByTwo(numbers)
+```
+## Longitud de cadena
+```sh 
+let NameLength = 0;
+const Name = "Lovelace";
+
+NameLength = Name.length;
+```
+## Push
+```sh
+let frutas = ["manzana", "banana", "cereza"];
+frutas.push("naranja");
+console.log(frutas); // ["manzana", "banana", "cereza", "naranja"]
+```
+## Arreglo
+```sh
+let arr = ["Pablo", "Lucas", "Juan",];
+console.log(arr[0]); // Pablo
+console.log(arr[2]); // Juan
+```
+## Map
+```sh
+let usuarios = [
+  {firstName : "Susan", lastName: "Steward"},
+  {firstName : "Daniel", lastName: "Longbottom"},
+];
+
+let nombresCompletos = usuarios.map(function(elemento) {
+    return `${elemento.firstName} ${elemento.lastName}`;
+});
+
+console.log(nombresCompletos);
+// ["Susan Steward", "Daniel Longbottom"]
+```
+##