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In this video I want to take a few minutes to explore another iOS 6 feature we're going to end up using

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to fix a problem with our current application.

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This is the default parameters syntax and that's going to allow us to set a default value for a function

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parameter should no argument be passed in.

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Now we'll explore this in isolation in the playground folder.

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Then we'll integrate it into the application to fix a problem with our code.

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So to kick things off we have one through six already in here.

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I'm going to create a new script seven and I'll call this something like.

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Default parameter dot J S.

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And in here we're gonna start with probably the most basic function example you'll ever see.

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Then we'll explore how we can improve it with default parameter values.

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Let's go ahead and create a greeter function over going to do is accept a name as the first and only

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parameter and then we're going to use it as part of a message we print down below.

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So something like console dialog Hello space followed by the person's name so I'll concatenate on using

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the plus operator the values stored in the name variable.

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Now if we go ahead and call this we know exactly what's gonna happen and down below I'll do just that.

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I'm going to call a greeter passing in a value for name.

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I'll go ahead and use my name.

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Andrew now from here we want to run the script so down below I am going to use controls C to shut down

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node mine and we're gonna switch from the web server folder to the playground directory so S.D. dot

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dot forward slash playground and once I'm inside of here I'm just gonna run the script.

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So that would be node space then 7 default parameters dot J S.

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Now when I run it I'm gonna see Hello andrew print.

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No surprise there.

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What I'm interested in though is what happens when I don't pass in an argument value to greeter.

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So right here all I'm gonna do is call greeter with no arguments.

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Now I'm gonna run the code once again and we're not going to get a javascript error.

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The program isn't going to crash but the result we do get is just as undesirable right here.

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When I run it we get.

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Hello undefined.

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So when the name is provided things go well when no name is provided.

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Obviously we can't use it but we could definitely do better than this.

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Instead of something like Hello undefined we could print something like Hello user or hello anonymous.

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Now the reason we're seeing undefined here is because that is the default value for a function parameter.

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If no argument is passed in none is provided here.

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So name is undefined and I see undefined in that message.

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Now obviously if we wanted to address this we could put an if statement inside of the greeter function

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to check if the name exists.

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If it does use it if it doesn't.

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Inside of an else clause we could print a completely different message but we can also use the default

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parameters syntax to achieve these same results with a lot less code and to set up a default value for

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a function parameter like name.

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All we do is use the equals sign right after it.

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So for the moment let's go ahead and add a second argument into the mix just so it's easy to visualize.

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So we take a name and we take an age.

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The goal is to set a default value for a name.

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What do we do.

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We go ahead and we use equals.

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Right after it followed by the default value we'd like to use.

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This could be anything.

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It could be a function an array an object a number a boolean or in our case a string.

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Now what name do we want to use by default.

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We could just use something generic like a user or anonymous or Hello person whatever you wanted to

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use as that default string.

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Now if I save things we can see how the program is going to function if an argument is provided that

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value will be used which means we'll still see.

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Hello Andrew.

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If no argument is provided then the default value will be used which means for the second printing we

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should see.

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Hello.

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User down below.

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I'm going to go ahead and rerun the program.

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After saving my file and that is exactly what I get I get Hello Andrew and Andrew is provided and I

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get Hello user when no name value was provided.

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Using this syntax makes it really easy to setup default values for your function parameters.

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There's one more thing I want to talk about before we jump back into apt.

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Jay asked and explore the issue we're going to address and what I want to talk about relates to dish

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structuring.

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So let's take a quick moment to open up that other playground file we created which was number five.

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Yes six objects in here we explored how we could use the object property shorthand and we explored how

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we could use object destruction bring we d structured as a standalone statement and we d structured

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function arguments like we saw with our transaction function down below now in this case we were dis

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structuring the second argument.

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So I was expecting it to be an object.

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Now currently it is an object we're passing in product.

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But what would happen if I didn't pass in any value we know the default value would be undefined.

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That's the value used if you don't pass anything in.

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So what happened when we try to ditch structure undefined right here we can see what's going to happen

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by running this script.

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So I've removed that second argument in the call to transaction and I'll run node 5.

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Yes six objects dot J.

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S and when I do I get a javascript error.

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Now the actual error message is cannot dish structure property label of undefined.

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So what it's talking about here is this line that is line 32 which it mentions right here.

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This is where we try to dish structure a parameter no value is passed in so undefined is used and we

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cannot dish structure undefined.

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Now we can easily address this by setting up a default parameter value.

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So here we are de structuring undefined because no object was provided if we wanted to fix this we could

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set a default value for that parameter equal to an empty object.

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Now we're always going to get an object whether it's passed in or whether the default object is used.

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Now let's run the program one more time to see what we get on line 33 when we log all three variables

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out down below.

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I'm gonna use the up arrow key and enter to rerun the previous command and what do I get for a name.

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I get Andrew for age I get twenty seven and location Philadelphia.

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That's coming from the first example for this console log.

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I get the type value of order for a label I get undefined end for stock I get undefined as well so here

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label and stock are both undefined because no object was provided.

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So we d structure to the empty object and this object has no label or stock property.

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So we see undefined for both.

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So by setting up this default object we can make sure that when we d structure and object the code works

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whether or not an object is ever passed in.

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Now from here you could take things even further when you're D structuring.

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You can also set up default values to use if you don't find a match.

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So in this case let's say that for a stock I want to use zero if no stock property exists on the object

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that's passed in like I would for a parameter.

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I just set up equals afterwords and I pick a value.

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Let's go ahead and use zero.

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Now if we rerun the program we're going to see that order still prints for type undefined still prints

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for a label and now stock is zero.

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Now once again we're only seeing zero because no object is provided.

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So we're de structuring an empty object.

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We try to grab stock off of that empty object it doesn't exist.

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So zero is used if I pass in product we are going to see the value up here.

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Two hundred and one.

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Let's go ahead and just demonstrate that I'll pass in product.

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I'll go ahead and rerun the program and I get order.

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Red notebook and two hundred and one.

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So in this case we pass an object in which means we're not de structuring the empty object ready structuring

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the object that was passed in that object does have a stock property.

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So the stock default value isn't used.

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And two hundred and one ends up printing.

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So that's just a little bit of information on a default parameters and how we can use those with D structuring.

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Now let's go ahead and get into the problem that we're running into in our program and to do this we

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are first going to head back over to the web server directory and start up our application once again.

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So for me that's going to be C D dot dot forward slash web server and once we're here we're going to

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rerun that node mod command that's no demand source a forward slash app dot and J.

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S and we're going to set up our extension list J S and H B S comma separated and then once we run that

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we can go ahead and use our application once again.

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Right here I refresh things and I'm going to get the updated forecast for Boston.

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Here we can see rain and windy starting in the evening and this is updated information.

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Now what happens if I don't provide an address where a match can be found.

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So if I provide as an example an exclamation mark we can see that we get an error.

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This site cannot be reached.

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And the problem is that our server actually crashed in the background.

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If we go ahead and scroll up what do we get.

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We got an error that we've seen before cannot dish structure property latitude of undefined.

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So in this case the geo code callback gets executed.

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We pass in a value for error and we don't pass in a value for the success data since it was not a success.

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We could not find a match.

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Error is provided in that case.

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Now the problem here is that we're still trying to ditch structure this object to fix that.

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All we do is we set up an empty object default value.

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Now the program is going to work as expected in both cases.

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So I'm going to add that on Save the file and down below we get our node man server restarting I'm gonna

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refresh the program and what do I get.

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I get my correct Jason response error unable to find location.

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Try another search.

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Now if I was to swap this out for a good location once again like Philadelphia this time I would still

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see what I'm expecting.

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My three properties with the forecast showing up.

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So by setting up a default object for the object we're trying to D structure we make sure that this

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code still works even if no data was provided.

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Now you might say.

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Doesn't that mean that latitude longitude and location would be undefined and you're right they would

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be undefined when I d structure them off of this empty object.

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But in that case we know error exists which means the only code that runs is this code and this code

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doesn't use those three values.

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That's only used down below when things went well.

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All right.

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That's a quick aside.

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Just fixing this little problem in our application.

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That's where we're gonna stop for this one.

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There will be some challenges throughout the class where will you will have to use the parameter default

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Value Syntax.

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So let's go ahead and jump back in and actually wire up the front end of our application to use this

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endpoint and allow the user to fetch whether from the browser.