Today we're going to start with a little test, then we'll go on to look at sorting and searching arrays.
We now have enough knowledge under our belts to attempt a typical JavaScript interview question known as FizzBuzz.
The first ten numbers, for example, would look like this:
1
2
"Fizz"
4
"Buzz"
"Fizz"
7
8
"Fizz"
You will often need to search an array in your programs, and there are a number of ways to achieve it in JavaScript.
The indexOf array method returns the index location of the item in question. Check it out:
let arr1 = [1, 'holy smokes', '007', "The name's Bond"];
const myIndex = arr1.indexOf('007');
console.log(arr1[myIndex]); // 007
Very cool! A nice easy way to get to the item. If it doesn't exist, the method will return -1.
The includes method is a very convenient method that returns a "truthy" result. By that, we mean the method will return true or false.
if (!arr1.includes('abcdefg')) {
console.log("Tell the user that the item doesn't exist...");
}
Note the use of of the "bang" operator to allow the if statement to return true if in fact the method can't find abcdefg (so a false actually becomes true).
Another useful method to search our array is the find method. This method employs a callback method to return the first value that satisfies the condition.
Knowledge of callbacks, filter and find is not required for the MTA exam.
let arr1 = [1, 2, 'holy smokes', '007', "The name's Bond"];
// arrow function
let result = arr1.find((el) => {
return el.toString().length < 5;
});
// older style function
let result = arr1.find(function (el) {
return el.toString().length < 5;
});
console.log(result); // 1
The last strategy we will look at is array.filter:
let arr1 = [1, 2, 'holy smokes', '007', "The name's Bond"];
let result = arr1.filter((el) => el.toString().length > 2);
console.log(result); // ["holy smokes", "007", "The name's Bond"]
Again, this employs a callback function. This time though, the filter method returns an array of all the matches. In the case above, we convert everything to a string, then check if the length is greater than two.
From time to time, you may need to sort your array. Thankfully, Sorting an array of strings in JavaScript is very straightforward:
let strings = ['Dan', 'Jim', 'Edy'];
strings.sort();
console.log(strings); // ["Dan", "Edy", "Jim"]
Thinking back to our conversation about primitives, why has the sort method changed the array directly?
Things start to fall apart a bit when we try and sort numbers:
let numbers = [1678, 2, 3, 78, 9, 10001];
numbers.sort();
console.log(numbers); // [10001, 1678, 2, 3, 78, 9]
How is JavaScript trying to sort the numbers above?
We can fix this by using a callback to examine the numbers in more detail:
numbers.sort(function (a, b) {
if (a > b) return 1; // switch numbers
if (a < b) return -1; // switch numbers
return 0; // numbers are the same
});