ERB array methods

const companies = [
    {name:"company one", category:"finance",start :1999, end:2004},
    {name:"company two", category:"retails",start :1982, end:2005},
    {name:"company three", category:"shipping",start :1983, end:2014},
    {name:"company four", category:"retail",start :2020, end:2024},
    {name:"company five", category:"finance",start :1985, end:2005},
    {name:"company six", category:"shipping",start :1986, end:2006},
    {name:"company seven", category:"catering",start :1987, end:2009},
    {name:"company eight", category:"finance",start :2012, end:2013},
    {name:"company nine", category:"catering",start :1989, end:2017},
    {name:"company ten", category:"finance",start :2020, end:2021},
    ];
const ages = [14,45,79,2,57,31,90,13,10,42];
//normal for loop//
// for (let i = 0; i < companies.length; i++){
//     console.log(companies[i].start);
// }
//for each method//
// companies.forEach(company=>(console.log(company.start)));
let total = 0;
ages.forEach((age,index,ages)=>ages[index] = ++age);
// console.log(ages);
//filter//
let adult = [];
for(let i=0;i<ages.length;i++){
    if (ages[i]>= 18){
        adult.push(ages[i]);
    }
}
// console.log(adult);
//array filter//
// let adults= ages.filter(age=>{
//     if(age>18){
//         return true;
//     }
// });
adults = ages.filter(age=>age>18);
// console.log(adults);
// const retailCompanies = companies.filter(company=>company.category=="retails");
// console.log(retailCompanies);
// const tenYears = companies.filter(company=>company.end - company.start >=10);
// console.log(tenYears);
const eighty = companies.filter(company=> company.start >= 1980 && company.start < 1990);
// console.log(eighty);
//map//
const testMap= companies.map(company=> `${company.name} [${company.start} - ${company.end}]`);
// console.log(testMap);
const ageMap = ages.map(age=>Math.sqrt(age)).map(age=>age*2);
// console.log(ageMap, ages);
//reduce//
const maxValue = (a,b)=>a>b ? a:b;
function maxSequence(a){
    let result = a[0];
    for (let e of a) result = maxValue(result,e);
    return result;
}
// console.log(maxSequence(ages));
const minValue = (a,b)=>a<b?a:b;
function minSequence(a){
    let result = a[0];
    for (let e of a) result = minValue(result,e);
    return result;
}
// console.log(minSequence(ages));
//extracting common sequence//
function reduce(array,func){
    let result = array[0];
    for (let element of array) result = func(result,element);
    return result;
}
// console.log(reduce(ages,maxValue));
// console.log(reduce(ages,minValue));
function reduce1(array,func,init){
    let result = init;
    for (let element of array) result = func(result,element);
    return result;
}
// console.log(reduce1(ages,minValue,1));
//js array reduce//
const ageSum = ages.reduce((total,age)=>{return total + age},0);
// console.log(ageSum);
const totalCompany = companies.reduce((acc,company)=>{return acc + company.end - company.start},0);
console.log(totalCompany);