I’m asked to get attributes collection out of an array object,

let a = [
    {name:'aname',age:21},
    {name:'bname',age:22},
    {name:'cname',age:23},
    {name:'dname',age:24},
    {name:'ename',age:25},
    {name:'fname',age:26},
    {name:'gname',age:27}]

// wanted
let ok = {
    names:'aname;bname;cname;dname;ename;fname;gname',
    ages:'21;22;23;24;25;26;27'
}

and I got 2 ways of doing it:

alpha just using map of an array:

// alpha
let res = {
    names:'',
    ages:''
}

res.names=a.map(iter=>iter.name).join(';')
res.ages=a.map(iter=>iter.age).join(';')
//then return res

// ========================================================

and beta just iterate the array and append each attribute in the tabulation array:

// beta
let res = {
    names:[],
    ages:[]
}

a.forEach(iter=>{
    res.names.push(iter.name)
    res.ages.push(iter.age)
})
// then handle res's fields
ok.names = res.names.join(';')
ok.ages = res.ages.join(';')

so which way should I use to get the collection? Will alpha get slower or faster than beta when the objects in a get lots of fields(attrs)?

>Solution :

Both approaches are good. I’d say it depends on your personal preference what you’d want to use.

However, It seems to me that if you are aiming for performance, the following would yield better results.

let a = [
    {name:'aname',age:21},
    {name:'bname',age:22},
    {name:'cname',age:23},
    {name:'dname',age:24},
    {name:'ename',age:25},
    {name:'fname',age:26},
    {name:'gname',age:27}]
    
let ok = { names: '', ages: ''}

for (let i = 0; i < a.length; i++){
const iter = a[i]
ok.names += iter.name + ";";
ok.ages += iter.age + ";";
}

ok.names = ok.names.slice(0,-1)
ok.ages = ok.ages.slice(0,-1)

console.log(ok)

This apporach eliminates the need to create new arrays or joining them (join is a heavy operation). Just create the string you want and at the end of it all, remove the one extra semicolon.