For...Of

When developing an application we inevitably need to iterate over a dataset. 0:00 For example, an Ajax request sends back a list of names or an array of objects. 0:05 And our program needs to go over each item in the array. 0:10 The array for each method provided in ES5 made looping over an array a breeze. 0:14 ES2015 gives us a similar but 0:19 slightly different technique the, the for of statements. 0:21 You can follow along by launching the workspace for this video. 0:26 So from the beginning of JavaScripts existence, we've relied heavily 0:29 on a basic for loop, where we determine the length of an array and 0:33 iterate by increment a variable by one for each pass. 0:37 For example let's take a look at the file for-loop.js containing a basic for loop. 0:40 If I run the file, the console logs the numbers one through six. 0:47 This works well enough but it's cumbersome. 0:51 Now ES5 gave us for each to process each item of an array in a callback function. 0:55 So if you wanted to control the loop to end it early, 1:01 we still had to use the for loop. 1:04 Now let's take a look at the file for-each.js which contains 1:07 a collection of teachers. 1:12 So say I wanted to log only Nick's rating to the console. 1:15 Well using for-each it would look something like this. 1:20 And when I run this code, I see Nick's rating in the console. 1:28 But what I don't see is how many times this function was called so 1:33 I'll add another log message outside of my if statement. 1:38 We'll say console.log teacher.name. 1:40 And you've probably already guessed that the names of online teachers will log 1:49 to the console. 1:53 So let's see. 1:54 And sure enough all nine teacher names are logged. 1:57 Luckily, ES2015 has a way to iterate over an array of values and 2:01 break out of the loop when needed. 2:07 So I'm going to rewrite the for 2:10 each loop using the new for of syntax by 2:14 typing for let teacher of teachers. 2:19 And now I can short circuit the loop or 2:26 break out of the loop after it logs Nick by using the break keyword. 2:29 So let's give it a try. 2:37 Over and the console, I'll run the code. 2:39 And now only seven teachers are logged 2:42 followed by Nicks rating which is exactly what I expected. 2:45 Keep in mind that for of can not be used with regular objects. 2:50 You'd want to use the for 2:55 in statement instead when looping over object properties. 2:57 So check the teachers notes to learn more about for in. 3:00 However, for of can be used with any interval object like strings, 3:04 arrays, maps, and sets. 3:09 Coming up in the next video we'll take a look at set, 3:12 a new type of iterable that lets you store unique values. 3:14