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Let's stick to functions.

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Another nice feature which is available in modern javascript is that you can assign default arguments

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to function parameters.

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Let's say you're in our add function.

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For some reason be one of a default value for b.

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So we know we want to be able to add two numbers together but in case you call this function with only

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one number we'll assume a default for the second argument or for the second parameter.

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We can do so by adding a equals on year in the parameter list and then setting our default value which

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of course has to match our type.

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For example 1 or whatever the default should be.

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And now it does enables us to call this function with only one argument so I could call it like this

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and typescript would not complain because it detects that we have a default argument here which is then

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taken for a b and therefore here I get output of 6 because my default B is 1 and I add 5 which makes

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6.

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Now one important note about default arguments here they have to be lost in the list.

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If you assign a default argument to a for example we'll have an issue why.

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Because default arguments are not skipped when you call a function.

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So if I call the function here with one argument then the arguments and passing in here are passed to

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the parameters in the same order.

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So calling the function with 1 argument 5 and this case passes does one argument to the first argument

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here in the parameter list and since the second argument is not provided with a default it's not optional

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and hence we provide no second argument at all.

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So typescript or JavaScript actually does not look at your function definition and guess that you probably

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want to skip the default argument and provide your value to the non default one.

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Instead it simply adheres to the order and therefore you should set defaults from the right.

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So make sure that the parameters for what you don't accept default arguments come first before your

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default parameters.