Some use cases of looping through an array in the functional programming way in JavaScript:

1. Just loop through an array

const myArray = [{x:100}, {x:200}, {x:300}];

myArray.forEach((element, index, array) => {
    console.log(element.x); // 100, 200, 300
    console.log(index); // 0, 1, 2
    console.log(array); // same myArray object 3 times
});

Note: Array.prototype.forEach() is not a functional way strictly speaking, as the function it takes as the input parameter is not supposed to return a value, which thus cannot be regarded as a pure function.

2. Check if any of the elements in an array pass a test

const people = [
    {name: 'John', age: 23}, 
    {name: 'Andrew', age: 3}, 
    {name: 'Peter', age: 8}, 
    {name: 'Hanna', age: 14}, 
    {name: 'Adam', age: 37}];

const anyAdult = people.some(person => person.age >= 18);
console.log(anyAdult); // true

3. Transform to a new array

const myArray = [{x:100}, {x:200}, {x:300}];

const newArray= myArray.map(element => element.x);
console.log(newArray); // [100, 200, 300]

Note: The map() method creates a new array with the results of calling a provided function on every element in the calling array.

4. Sum up a particular property, and calculate its average

const myArray = [{x:100}, {x:200}, {x:300}];

const sum = myArray.map(element => element.x).reduce((a, b) => a + b, 0);
console.log(sum); // 600 = 0 + 100 + 200 + 300

const average = sum / myArray.length;
console.log(average); // 200

5. Create a new array based on the original but without modifying it

const myArray = [{x:100}, {x:200}, {x:300}];

const newArray= myArray.map(element => {
    return {
        ...element,
        x: element.x * 2
    };
});

console.log(myArray); // [100, 200, 300]
console.log(newArray); // [200, 400, 600]

6. Count the number of each category

const people = [
    {name: 'John', group: 'A'}, 
    {name: 'Andrew', group: 'C'}, 
    {name: 'Peter', group: 'A'}, 
    {name: 'James', group: 'B'}, 
    {name: 'Hanna', group: 'A'}, 
    {name: 'Adam', group: 'B'}];

const groupInfo = people.reduce((groups, person) => {
    const {A = 0, B = 0, C = 0} = groups;
    if (person.group === 'A') {
        return {...groups, A: A + 1};
    } else if (person.group === 'B') {
        return {...groups, B: B + 1};
    } else {
        return {...groups, C: C + 1};
    }
}, {});

console.log(groupInfo); // {A: 3, C: 1, B: 2}

7. Retrieve a subset of an array based on particular criteria

const myArray = [{x:100}, {x:200}, {x:300}];

const newArray = myArray.filter(element => element.x > 250);
console.log(newArray); // [{x:300}] 

Note: The filter() method creates a new array with all elements that pass the test implemented by the provided function.

8. Sort an array

const people = [
  { name: "John", age: 21 },
  { name: "Peter", age: 31 },
  { name: "Andrew", age: 29 },
  { name: "Thomas", age: 25 }
];

let sortByAge = people.sort(function (p1, p2) {
  return p1.age - p2.age;
});

console.log(sortByAge);

9. Find an element in an array

const people = [ {name: "john", age:23},
                {name: "john", age:43},
                {name: "jim", age:101},
                {name: "bob", age:67} ];

const john = people.find(person => person.name === 'john');
console.log(john);

The Array.prototype.find() method returns the value of the first element in the array that satisfies the provided testing function.

References

• Array.prototype.some()
• Array.prototype.forEach()
• Array.prototype.map()
• Array.prototype.filter()
• Array.prototype.sort()
• Spread syntax
• Array.prototype.find()

You should use flatMap first because you have will change the number of elements (you start with 2, you end with 3) and inside a simple map to convert 1:1 each project into your final object.

Working Demo

const data = [{
    "title": "Release",
    "projects": [{
      "name": "Server",
      "result": {
        "success": 0,
        "failure": 100
      },
    }]
  },
  {
    "title": "Payments",
    "projects": [{
        "name": "Platform1",
        "result": {
          "success": 100,
          "failure": 0
        }
      },
      {
        "name": "Platform2",
        "result": {
          "success": 50,
          "failure": 50,
        }
      }
    ]
  }
];

var groupedData = data.flatMap((el) =>
  el.projects.map((proj) => ({
    name: el.title + "-" + proj.name,
    success: proj.result.success,
    failure: proj.result.failure,
  }))
);

console.log(groupedData);

You can use forEach method to iterate over array of objects.

data.messages.forEach(function(message){
    console.log(message)
});

Refer: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach