Defining a Variable with let2:48 with Andrew Chalkley
Using constants is are a best practice when assigning variables but what happens when you do actually want to reassign a value? That's where let comes in.
The let keyword is used when you want to re-assign a variable. 0:00 In that respect, it just works like var. 0:04 Let's take a look at a simple example. 0:07 Open up let.html, and you can see we've got a score that equals 0, 0:10 an age that equals 33, and a Boolean, isHungry, that equals false. 0:15 Open up the preview, and navigate to let.html. 0:22 Open up the Console, And let's try and modify the score. 0:29 The score can change through a game, 0:36 the score increments by one each time the player completes a challenge. 0:38 Again, let just works like var, 0:43 you can re-assign values to a variable that is declared with the let keyword. 0:47 You can update the age to be 34, and 0:53 isHungry, To be true. 0:58 Let's look at a more complex example, 1:08 where you should use let rather than a const. 1:11 Open up person.html, and here we have a function called personDescription. 1:14 That creates a description string that gets logged out at the end here. 1:21 If the person object has a role, 1:27 It will add additional information at the end of the description, and is logged out. 1:33 Let's see this in action. 1:40 Go to the preview, click on person.html, 1:42 open up the developer console, and we should see Andrew is a Teacher. 1:46 If we change the var keyword in the person description function to const, 1:52 And run it again, we get an error, 1:59 because we're trying to re-assign the description in the if block. 2:01 We could change it to var, 2:10 or alternatively we could use the new let keyword. 2:12 Let works like var, allowing you to re-assign variables, but 2:18 unlike var it has block level scoping. 2:23 We'll explore when we'd see the advantages of using let over var in the next video. 2:26 Now that we've changed the constant to let, 2:32 let's see how it works in our browser. 2:34 Looking in the console, we see Andrew is a Teacher printed out like we expect. 2:38 In the next video, 2:42 we'll look at how let solves some problems where the var keyword falls short. 2:43
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