• Strengthen your JavaScript skills by using those array methods!

The some() method tests whether at least one element in the array passes the test implemented by the provided function. It returns true if it finds an element returns true for the provided function. Otherwise it returns false.

Note that it doesn't modify the array.

const people = [
      { name: 'Wes', year: 1988 },
      { name: 'Kait', year: 1986 },
      { name: 'Irv', year: 1970 },
      { name: 'Lux', year: 2015 }
    ];

Here we have an array of some people's information. Let's say we want to check if there's at least one person in the array that is 19 or older.

First we get the current year from a new Date object, so we can calculate the age of each person. If a person's age is 19 or greater than 19, the function will return true. Since there are three people that are over 19 in the array, isAdult is true.

const isAdult = people.some(person => {
      const currentYear = (new Date()).getFullYear();
      if (currentYear - person.year >= 19) {
        return true;
      }
    });

console.log(isAdult); // true

The code can be simplified into one line:

const isAdult = people.some(person => (new Date()).getFullYear() - person.year >= 19);

Very similar to some() method, but every() method only returns true if all elements in the array pass the test implemented by the provided function. It returns a Boolean value.

Let's say this time we want to check if every person in the array are 19 or older. In this array, there's one person that is under 19, so isAllAdult will be false.

const isAllAdult = people.every(person => {
      const currentYear = (new Date()).getFullYear();
      if (currentYear - person.year >= 19) {
        return true;
      }
    });
console.log(isAllAdult); // false

The find() method returns the first element in the provided array that satisfies the provided testing function. If no values satisfy the testing function, undefined is returned.

const comments = [
      { text: 'Love this!', id: 523423 },
      { text: 'Super good', id: 823423 },
      { text: 'You are the best', id: 2039842 },
      { text: 'Ramen is my fav food ever', id: 123523 },
      { text: 'Nice Nice Nice!', id: 542328 }
    ];

Here we have an array of different comments labeled with ids. Let's say we want to find the comment whose id is 823423. The method will return the first element that matches the statement, which is the second comment 'Super good'.

const comment = comments.find(comment => {
      if (comment.id === 823423) {
        return true;
      }
    });
console.log(comment); // Object { text: "Super good", id: 823423 }

The code can be simplified into one line:

const comment = comments.find(comment => comment.id === 823423);

The find() method is very similar to filter(), however, filter() returns an ARRAY of ALL elements that matches the statement. While find() only returns the first ELEMENT that matches.

If using filter() in this situation, we will get an array containing one single element.

const comment_filter = comments.filter(comment => {
      if (comment.id === 823423) {
        return true;
      }
    });
console.log(comment_filter); 
// Array [ { text: "Super good", id: 823423 } ]

The findIndex() method returns the index of the first element in an array that satisfies the provided testing function. If no elements satisfy the testing function, -1 is returned.

Let's say we want to find the index of the comment whose id is 823423, then delete it from the comments. By using findIndex() method, we now know the index of the comment is 1.

const index = comments.findIndex(comment => comment.id === 823423);
console.log(index); // 1

There are two ways to delete the comment from the array. The first way is by using splice().

comments.splice(1, 1);
console.log(comments); // Array(4) [ {…}, {…}, {…}, {…} 

However, the splice() will mutate the original array. If we don't want to mutate the original array, we can use slice() instead. Don't forget to use the spread(...) syntax to spread all the elements in the array.

const newComments = [
      ...comments.slice(0, index),
      ...comments.slice(index)
    ];
console.log(newComments) // Array(4) [ {…}, {…}, {…}, {…} ]

• Array.prototype.some() - MDN
• Array.prototype.every() - MDN
• Array.prototype.find() - MDN
• Array.prototype.findIndex() - MDN