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Introducing ES2015

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Default Parameters

2:51 with Guil Hernandez and Ken Howard

Finally we’re able to set default values for function parameters like every other programming language. We’ll review just how simple it is to use.

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    Another feature of VS2015 is default parameters. 0:00
    Default parameters let you set default values for 0:04
    parameters accepted by a function. 0:06
    If you're familiar with other programming languages you're probably 0:08
    already familiar with the concept. 0:11
    You can call a function and if you don't pass a value for 0:13
    certain parameters the function can fill in those blanks with the default values. 0:16
    You can follow along using the latest workspace by 0:21
    launching the workspace on this page. 0:23
    Suppose we have a function. 0:25
    We'll call it greet. 0:27
    It takes two parameters, name and time of day, and it logs a message to the console. 0:28
    Now in ES5, we could check the arguments passed into the function and 0:34
    set default values. 0:38
    So for example we can say name = name | | 'guil' and 0:40
    time of day = time of day double pipe day. 0:48
    So here the double pipe checks the variable. 0:54
    And returns the value of the variable. 0:56
    If it's true, the otherwise it returns the default value on the right side. 0:59
    If I call this greet function and run the file in the console. 1:06
    I see the message Good Day, Guil! 1:12
    In ES 2015 we can set default values for 1:14
    the parameters we pass to a function simply by adding an equal sign in a value. 1:18
    So I'll delete the name and time of day variables a nd values I just wrote. 1:23
    And right up here, the values we pass can be a string, 1:29
    Boolean, object, array or a function. 1:33
    So, in this case, let's give our parameters strings for default values. 1:36
    So we'll say name = Guil and time of day = day. 1:40
    So, now even when I don't provide a name or time of day. 1:51
    The council will still log. 1:56
    Good Day, Guil to the console. 1:57
    So, now let's try something different. 2:00
    I'm okay with the default value for a name but 2:02
    I wanna provide my greeting a different value for time of day. 2:06
    To do this, I need to pass the function undefined as the value for 2:11
    the name parameter. 2:16
    You see, parameters with a default value are considered optional. 2:18
    So we pass undefined to tell the interpreter to use the default value. 2:23
    And then I'll set the second parameter to afternoon. 2:28
    So now when I run the file in the console, it logs the message, good afternoon Guil. 2:34
    Why thank you, console. 2:39
    Default parameters are easy to start using, and 2:42
    will help your code be readable and maintainable in the future. 2:44
    In the next video I'll teach you about rest parameters and spread operators. 2:47

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