Question 235774 in Javascript Question posted in
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Javascript – Confused how to work with .map or .reduce or foreach

I am new to JavaScript. I am little confused even after reading multiple answers and Mozilla.org docs… My issue is that if there’s a simple array I am able to use .map,.filter easily but if array has objects then it becomes a little confusing.

E.g. – I have to add all ages here.

I know .map might not work as it gives a new array (which I don’t want here), .filter won’t work (that’s for returning elements that satisfy given condition), forEach don’t returns anything.

I am not allowed to use for loop but that’s the most convenient here (Below code is correct & working).

How else can I solve it?

const users=[
  {firstName:"john",lastName:"Biden",age:26},
  {firstName:"jimmy",lastName:"cob",age:75},
  {firstName:"sam",lastName:"lewis",age:50},
  {firstName:"Ronald",lastName:"Mathew",age:26},  
];
var total=0
//console.log(users.length)
for(let i=0;i<users.length;i++){
    //console.log(users[i].age)
   total+=users[i].age
}

console.log(total)
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2

Answers


  1. 0

    You can use forEach where you use the for

    You can use map to make an array of ages and reduce it to sum it

    You can use filter to count only those above or equal to 50 years of age

    The ({age}) is using destructuring to get a just the age of the object array as an alternative to total=users.map(item => { return item.age })

    const users=[
  {firstName:"john",lastName:"Biden",age:26},
  {firstName:"jimmy",lastName:"cob",age:75},
  {firstName:"sam",lastName:"lewis",age:50},
  {firstName:"Ronald",lastName:"Mathew",age:26},  
];

// forEach needs the total initialised

let total=0
users.forEach(user => total+=user.age)
console.log(total)

// map plus reduce (to sum) does not need to initialise

total=users.map(({age}) => age)
.reduce((a,b) => a+b)
console.log(total)

// filter plus reduce also does not need initialising the total

let total50Plus=users.filter(({age}) => age>=50)
.reduce((a,b) => a.age+b.age)   // does not need an accumulator initialised
console.log(total50Plus)

// the standard reduce initialises the accumulator at the end of the function

total=users.reduce((acc,{age}) => acc+=age,0);  
console.log(total)

// full version 

total=users.reduce((accumulator, current) => {
  accumulator += current.age;
  return accumulator;
},0); // initialise the accumulator 
console.log(total)
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  2. 0

    Using ForEach it will be practical to manipulate your array of objects.
    Understand the parameters used in the forEach callback:

    currentValue (user)

    The current value of the element being processed in the array.

    optional index

    The index of the current element being processed in the array.

    optional array

    The array that forEach() is being applied to.

    In the example below follows the code of what you want using forEach.

    const users = [
  {firstName:"john",lastName:"Biden",age:26},
  {firstName:"jimmy",lastName:"cob",age:75},
  {firstName:"sam",lastName:"lewis",age:50},
  {firstName:"Ronald",lastName:"Mathew",age:26},  
];

let total = 0;

users.forEach(function(user, index, array) {
    total += user.age;
});

console.log(total);
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