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.
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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