I have an object that looks like this:

let arr = {
  names: ['John', 'Paul'],
  phones: ['iPhone', 'Samsung', 'Huawei'],
  clothesBrands: ['HM', 'Zara']
}

I have an object that looks like this:

let arr = {
  names: ['John', 'Paul'],
  phones: ['iPhone', 'Samsung', 'Huawei'],
  clothesBrands: ['HM', 'Zara']
}

I need to sum the lengths of the arrays. I can do it like this:

arr.names.length + arr.phones.length + arr.clothesBrands.length 

and the result is 7.

How can I do it in a clean way if I don't know all the keys?

• javascript
• arrays

• Will the key values always be an array? – Spangle Commented Feb 22, 2019 at 5:37

7 Answers 7

You can check the length of the .flattened array of values:

const arr = {
  names: ['John', 'Paul'],
  phones: ['iPhone', 'Samsung', 'Huawei'],
  clothesBrands: ['HM', 'Zara']
};

console.log(Object.values(arr).flat().length);

You can use object.values and reduce

Object.values will give you all the values in Object and with reduce we calculate total length.

let obj = {names: ['John', 'Paul'], phones: ['iPhone', 'Samsung', 'Huawei'], clothesBrands: ['HM', 'Zara']}

let op = Object.values(obj).reduce( (out, inp) => out + inp.length, 0)

console.log(op)

Use reduce . Get all the values in the objects and in reduce add the lengths of the arrays one by one

var arr = {
  names: ['John', 'Paul'],
  phones: ['iPhone', 'Samsung', 'Huawei'],
  clothesBrands: ['HM', 'Zara']
}
console.log(Object.values(arr).reduce((acc, e) => acc += e.length, 0))

You can use Array.prototype.reduce()on Object.values and check whether the value is array by Array.isArray()

let obj ={names: ['John', 'Paul'], phones: ['iPhone', 'Samsung', 'Huawei'], clothesBrands: ['HM', 'Zara']}
let sum = Object.values(obj).reduce((ac,a) => {
  return Array.isArray(a) ? ac + a.length : ac
},0)
console.log(sum);

For in loops are your friend when working with objects. Example to solve your problem below:

var arr = {names: ['John', 'Paul'], phones: ['iPhone', 'Samsung', 'Huawei'], clothesBrands: ['HM', 'Zara'], hello: 1};

var totalLength = 0;

for(var char in arr){
  // Confirm that the key value is an array before adding the value.
  if(Array.isArray(arr[char])){
    totalLength += arr[char].length;	
  }
}
console.log(totalLength);

Hopefully this helps.

Here you have another alternative using for ... in to iterate over the object keys directly:

let arr = {
  names: ['John', 'Paul'],
  phones: ['iPhone', 'Samsung', 'Huawei'],
  clothesBrands: ['HM', 'Zara']
}

let totalLen = 0;

for (k in arr)
{
    Array.isArray(arr[k]) && (totalLen += arr[k].length);
}

console.log(totalLen);

You should use Array.reduce for this.

const arr = {names: ['John', 'Paul'], phones: ['iPhone', 'Samsung', 'Huawei'], clothesBrands: ['HM', 'Zara']};

const sum = Object.values(arr).reduce((acc, {length}) => {
 return acc = length ? acc+ length : acc; 
}, 0);
console.log(sum);