JSFiddle - React, Tailwind, and code Playground

JavaScript

var str = '[ ' +  
    '  {"key": "113", "id":"113","title":"Coal","hex":"4f4f4f"}, ' + 
    '  {"key": "116", "id":"116","title":"White","hex":"fdfbf7"}, ' + 
    '  {"key": "115", "id":"115","title":"Greylead","hex":"b3b3b3"} ' + 
    ']';
var arr = JSON.parse(str);
var keys = [];
for (var i = 0; i < arr.length; i++)
    keys.push(arr[i].key);
alert(keys);