How to map array of object

Question

I have my array of object "messages" i want to calculate the number of items that have "seen:1"

const messages = [ 

 { id: 66, seen:1, tourist_full_name: "Khouloud Ben Abddallah" },
 { id: 102, seen: 0, tourist_full_name: "Harry Paz Galvez" },
{ id: 103, seen: 0, tourist_full_name: "Harry Paz Galvez" },
 { id: 104, seen: 1, tourist_full_name: "Harry Paz Galvez" },
{ id: 105, seen: 1, tourist_full_name: "Harry Paz Galvez" }
];

for example here i want to create a variable that can be like this

var SeenCount=3 ;

how can i do that ?

use js filter to solve this: messages.filter(function(msg) { return msg.seen === 1; }) — Sarvesh Mahajan, Dec 10 '19 at 16:15

score 1 · Answer 1 · answered Dec 10 '19 at 16:17

Use the reduce function to increment based on the seen property of each object. Our default value is 0 and it will increment in each iteration of our loop depending on the seen property value

const messages = [ 

 { id: 66, seen:1, tourist_full_name: "Khouloud Ben Abddallah" },
 { id: 102, seen: 0, tourist_full_name: "Harry Paz Galvez" },
{ id: 103, seen: 0, tourist_full_name: "Harry Paz Galvez" },
 { id: 104, seen: 1, tourist_full_name: "Harry Paz Galvez" },
{ id: 105, seen: 1, tourist_full_name: "Harry Paz Galvez" }
];


let a = messages.reduce((acc, item) => {
  return acc + item.seen;
}, 0);

console.log(a);

How to map array of object

1 Answers1