Javascript Concat Values of Two Arrays

Question

I have two arrays like this:

const a = ['a', 'b', 'c', 'd'];
const b = ['1', '2', '3', '4'];

I'm trying to make a new array like this:

const c = ['a1', 'b2', 'c3', 'd4'];

I tried it this way:

const c = [];
c.push([`${a[0]}${b[0]}`, `${a[1]}${b[1]}`, `${a[2]}${b[2]}`, `${a[3]}${b[3]}`]);

With actually looping through data and doing this took 17400ms.

I took out the c.push([........]); and it dropped to 1250ms.

Why does this take so long to do?

And what is the best way to do this?

Answer 1

you can use .map to achieve that. map a, then use index on each loop to get element of b.

const a = ['a', 'b', 'c', 'd'];
const b = ['1', '2', '3', '4'];

var c = a.map(function (d, i) {
    return d + String(b[i])
})

console.log(c)
// ["a1", "b2", "c3", "d4"]

cleaner code using es6:

var c = a.map((d, i) => `${d}${b[i]}`)

Answer 2

A simple loop.

const a = ['a', 'b', 'c', 'd', 'e'];
const b = ['1', '2', '3'];
var result = [];

for (var i = 0; i < a.length; i++) {
  result[i] = a[i] + b[i];
}

alert(result);