Functions defined by function expressions and function declarations are parsed only once, while those defined by the Function constructor are not. That is, the function body string passed to the Function constructor must be parsed each and every time the constructor is called. Although a function expression creates a closure every time, the function body is not reparsed, so function expressions are still faster than " new Function Therefore the Function constructor should generally be avoided whenever possible.
It should be noted, however, that function expressions and function declarations nested within the function generated by parsing a Function constructor 's string aren't parsed repeatedly. A function declaration is very easily and often unintentionally turned into a function expression. A function declaration ceases to be one when it either:. In strict mode , starting with ES, functions inside blocks are now scoped to that block.
Prior to ES, block-level functions were forbidden in strict mode. ES says that if shouldDefineZero is false, then zero should never be defined, since the block never executes. However, it's a new part of the standard. Historically, this was left unspecified, and some browsers would define zero whether the block executed or not. In strict mode , all browsers that support ES handle this the same way: zero is defined only if shouldDefineZero is true, and only in the scope of the if -block.
A safer way to define functions conditionally is to assign a function expression to a variable:. The following function returns a string containing the formatted representation of a number padded with leading zeros.
You can determine whether a function exists by using the typeof operator. In the following example, a test is performed to determine if the window object has a property called noFunc that is a function. If so, it is used; otherwise, some other action is taken. Note that in the if test, a reference to noFunc is used—there are no brackets " " after the function name so the actual function is not called.
There is a special syntax for declaring functions see function statement for details : function name [ param [ , param [ , All do approximately the same thing, with a few subtle differences: There is a distinction between the function name and the variable the function is assigned to.
In a word: Don't. In non-strict code, function declarations inside blocks behave strangely. Logical nullish assignment?? Object initializer Operator precedence Optional chaining?. Warning: JavaScript 1. This can generally be resolved by dropping the default value. This usage remains allowed, though it is recommended to use an explicit nullable type instead. By default, function arguments are passed by value so that if the value of the argument within the function is changed, it does not get changed outside of the function.
To allow a function to modify its arguments, they must be passed by reference. Example 4 Passing function parameters by reference. It is an error to pass a value as argument which is supposed to be passed by reference. Example 5 Use of default parameters in functions. PHP also allows the use of array s and the special type null as default values, for example:. Example 6 Using non-scalar types as default values.
The default value must be a constant expression, not for example a variable, a class member or a function call. Note that when using default arguments, any defaults should be on the right side of any non-default arguments; otherwise, things will not work as expected. Consider the following code snippet:. Example 7 Incorrect usage of default function arguments.
Example 8 Correct usage of default function arguments. Note : Arguments that are passed by reference may have a default value. PHP has support for variable-length argument lists in user-defined functions by using the This technique is not recommended as it was used prior to the introduction of the Argument lists may include the The arguments will be passed into the given variable as an array; for example: Example 9 Using You may specify normal positional arguments before the In this case, only the trailing arguments that don't match a positional argument will be added to the array generated by Occasionally it is necessary to define a function that takes an arbitrary number of parameters of heterogeneous type.
It would not be practical to create all the possible overloaded methods to account for all the types that could be used. NET implementations provide support for such methods through the parameter array feature.
A method that takes a parameter array in its signature can be provided with an arbitrary number of parameters. The parameters are put into an array. The type of the array elements determines the parameter types that can be passed to the function. If you define the parameter array with System. Object as the element type, then client code can pass values of any type. In F , parameter arrays can only be defined in methods. They cannot be used in standalone functions or functions that are defined in modules.
You define a parameter array by using the ParamArray attribute. The ParamArray attribute can only be applied to the last parameter.
The following code illustrates both calling a. NET method that takes a parameter array and the definition of a type in F that has a method that takes a parameter array. Feedback will be sent to Microsoft: By pressing the submit button, your feedback will be used to improve Microsoft products and services. Privacy policy. Skip to main content.
This browser is no longer supported. Download Microsoft Edge More info. Contents Exit focus mode. Is this page helpful? We will use the content of x and combine it with "Good morning" to say hello to a specific person.
If we do not specify it, we will run into an error as the function expects that we do hand over this argument. Again, as we have no explicit return, the function will return the last thing returned internally, which is again the NULL value from cat. However, in contrast to function A we now have a flexible function which can be used to say hello to anyone we like to. Try and see what happens if you use an integer, a logical value, and a character vector as input argument e.
As you will see, the function still works — even if the result might be a bit strange "Good morning TRUE". The reason is that our input argument is simply forwarded to the paste function, and the paste function is able to handle all these cases without any problem. This function is not very specific. In reality, we might extend the function and check what is specified on the input argument x such that we can throw an error if the input is, e. Let us declare a new function which we will call hello for now.
This function no longer uses cat , so it does not automatically show the result. Instead we are using paste to create the welcome message, and then return that character to be used outside the function.
Instead we get the resulting character string "Hi Peter" returned by our function. Both functions do the same, except that one uses return for the return value, the other one invisible and use "Hi" , and "Hello" , respectively. Invisible returns are used frequently in R by a wide range of functions. One example is the function boxplot. Typically, one is only interested in the figure, wherefore it is not necessary that boxplot returns anything. However, there is an invisible return which contains the numeric values used to create the plot.
An example using some random data:. The function returns a list with all the components used for plotting. So far, our functions always returned a character string. A function can, of course also print one thing, and return something else. Let us create one last function in this section.
When calling the function we now expect that the character string is printed, and that the function returns the number of characters letters in this string. Let us try:. When calling the function, we can immediately see "Hello Max". This is caused by calling cat inside the function.
But let us see what the function returned. What we get in return is an integer vector which contains 9. In R , things can sometimes be written in slightly different ways, which also yields for function definitions.
Brackets and explicit returns version 1 are typically preferred. For very short functions as this one, one-liner versions can also be OK. So far, our function s always only had one single input argument. More often than not, functions come with multiple arguments. Let us extend the function from above the hello function and add a second argument which will be called greeting.
The first argument main input is often called x or object , we will stick to x here. Both arguments are required arguments. When calling the function, we must specify both. As in the function declaration, the arguments are separated by a comma ,.
Remark : Why this strange order of input arguments? Well, we could also change the order and define the function as follows new function hello2 :. As you can see, both functions do the very same, except that the input arguments are flipped. What if we forget to properly specify all required arguments? In this case R throws an error and tells us which one was missing here greetings.
Again, R is very precise to tell us what has been going wrong — try to get used to properly read error messages. But : This only causes an error if the argument is evaluated in the function. If not used at all, no error will be thrown. In this case the additional argument prefix is never used in the instructions. In such a situation there will be no error.
This is, however, a very bad example to follow — if there are input arguments they should also be used in some way. When calling functions, the arguments to the function can be named or unnamed. Named arguments are always matched first, the remaining ones are matched by position. All unnamed : When calling the function with two unnamed input arguments, the arguments are used in this order the first one will be x , the second one greeting.
All named : Alternatively, we can always name all arguments. In case we name both, the order does not matter as R knows which one is which one. Mixed : If we mix named and unnamed arguments, the named ones are matched first. The rest unnamed arguments are used for the remaining function arguments in the same order as we provide them. First, the named one greeting is matched. The second unnamed argument "Rob" is then used for the remaining input arguments we have not explicitly defined.
All left is our input x , thus "Rob" is used as x.
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