Array.prototype.join

const employees = [
{
"firstName": "Arabela",
"lastName": "Fockes",
"email": "afockes0@wired.com",
"salary": "$6.18",
"isEngineer": true,
"gender": "Female"
},
{
"firstName": "Bryant",
"lastName": "Marchi",
"email": "bmarchi1@theatlantic.com",
"salary": "$8.05",
"isEngineer": false,
"gender": "Male"
},
{
"firstName": "Batholomew",
"lastName": "Eim",
"email": "beim2@goodreads.com",
"salary": "$7.26",
"isEngineer": true,
"gender": "Male"
}
];

[object Object], [object Object], [object Object]

const employees = [
    {
        "firstName": "Arabela",
        "lastName": "Fockes",
        "email": "afockes0@wired.com",
        "salary": "$6.18",
        "isEngineer": true,
        "gender": "Female"
    },
    {
        "firstName": "Bryant",
        "lastName": "Marchi",
        "email": "bmarchi1@theatlantic.com",
        "salary": "$8.05",
        "isEngineer": false,
        "gender": "Male"
    },
    {
        "firstName": "Batholomew",
        "lastName": "Eim",
        "email": "beim2@goodreads.com",
        "salary": "$7.26",
        "isEngineer": true,
        "gender": "Male"
    }
]
console.log(employees.join(', '))

let f1 = function() {
    return 'from f1'
}
let myArray = [1, 2, null, undefined, 5, true, {}, 'str', f1()]
 
Array.prototype.myJoin = function(sep) {
    let len = this.length
    if(sep) {
        sep = sep        
    } else {
        sep = ','
    }
    let s = ''
    let k = 0
    while(k<len) {
        if(k>0) {
            s += sep
        }
        let el = this[k]
        if(el === undefined || el === null) {
            var next = ''
        } else {
            next = el
        }
        s += next
        k++
    }
    return s
}
 
console.log(myArray.join())   // 1,2,,,5,true,[object Object],str,from f1
console.log(myArray.myJoin()) // 1,2,,,5,true,[object Object],str,from f1