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Defining Variables with let and const

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Defining a Variable with let

2:48 with Andrew Chalkley

Using constants 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.

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    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 the score = 0 and 0:09
    age = 33, and a boolean is hungry = false. 0:16
    Open up the preview and navigate to let.html. 0:22
    Open up the console, and let's try and modify the score. 0:28
    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 reassign values to a variable that is declared with the let keyword. 0:47
    You can update the age to be 34. 0:53
    And is hungry. 0:57
    To be true. 1:05
    Let's look at a more complex example where you should use let rather than a const. 1:07
    Open up person.html, and here we have a function called 1:14
    personDescription that creates a description string. 1:18
    That gets logged out at the end here. 1:24
    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. 1:42
    Click on person.html, 1:43
    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, because we're trying to re-assign the description 1:59
    in the if block, We could change it to var, 2:06
    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 const to let, let's see how it works in our browser. 2:32
    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 solved some problems where the var keyword falls short. 2:43

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