Default parameters

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Default function parameters allow formal parameters to be initialized with default values if no value or undefined is passed. The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https: In JavaScript, parameters of functions default to sbicap securities account opening charges. However, in some situations it might be useful to set a different default value.

This is where default parameters can help. In the past, the general strategy for com optional parameters defaults was to test parameter values in the body of the function and assign a value if they are undefined. However, this is caught with the second line in this example:. With default parameters in ES, the check in the function body is no longer necessary.

Now, you can simply put 1 as com optional parameters default value for b in the function head:. In the second call here, even if the second argument is set explicitly to undefined though not null or other falsy values when calling, the value of the num argument is the default one. The default argument gets evaluated at call time, so unlike e. This functionality is approximated in a straight forward fashion and demonstrates how many edge cases are com optional parameters.

Default parameters are always executed first, function declarations inside the function body evaluate afterwards. Parameters are still set left-to-right, overwriting default parameters even if there are later parameters without defaults. You can use default value assignment with the destructuring assignment notation:. Get the latest and greatest from MDN delivered straight to your inbox.

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If you'd like to contribute to the data, please check out https: Feature Chrome Edge Firefox Internet Explorer Opera Safari Basic support 49 14 15 No com optional parameters 10 Parameters without defaults after default parameters 49 14 26 No 36 10 Destructured parameter with default value assignment 49? Parameters com optional parameters defaults after default parameters 49 49 14 26 36 10?

Destructured parameter with default com optional parameters assignment 49 49? Full support Yes Destructured parameter with default value assignment Full support 49? Full support 41 No support No? Full support 49 Full support 49? Document Tags and Contributors Tags: Contributors to this page: Learn the best of web development Get the latest and greatest from MDN delivered straight to your inbox.

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You can specify that a procedure parameter is optional and no argument has to be supplied for it when the procedure is called. Optional parameters are indicated by the Optional keyword in the procedure definition.

The following rules apply:. Every parameter following an optional parameter in the procedure definition must also be optional. When you call a procedure with an optional parameter, you can choose whether to supply the argument. If you do not, the procedure uses the default value declared for that parameter. When you omit one or more optional arguments in the argument list, you use successive commas to mark their positions. The following example call supplies the first and fourth arguments but not the second or third:.

The following example makes several calls to the MsgBox function. MsgBox has one required parameter and two optional parameters. The first call to MsgBox supplies all three arguments in the order that MsgBox defines them. The second call supplies only the required argument.

The third and fourth calls supply the first and third arguments. The third call does this by position, and the fourth call does it by name. A procedure cannot detect at run time whether a given argument has been omitted or the calling code has explicitly supplied the default value.

If you need to make this distinction, you can set an unlikely value as the default. The following procedure defines the optional parameter office , and tests for its default value, QJZ , to see if it has been omitted in the call:.

If the optional parameter is a reference type such as a String , you can use Nothing as the default value, provided this is not an expected value for the argument. Another way to define a procedure with optional parameters is to use overloading. If you have one optional parameter, you can define two overloaded versions of the procedure, one accepting the parameter and one without it.

This approach becomes more complicated as the number of optional parameters increases. However, its advantage is that you can be absolutely sure whether the calling program supplied each optional argument. The feedback system for this content will be changing soon. Old comments will not be carried over. If content within a comment thread is important to you, please save a copy. For more information on the upcoming change, we invite you to read our blog post.

The following rules apply: Every optional parameter in the procedure definition must specify a default value. The default value for an optional parameter must be a constant expression. The following syntax shows a procedure declaration with an optional parameter: The following example call supplies the first and fourth arguments but not the second or third: Sub name argument 1, , , argument 4 The following example makes several calls to the MsgBox function.

The following procedure defines the optional parameter office , and tests for its default value, QJZ , to see if it has been omitted in the call: End Sub If the optional parameter is a reference type such as a String , you can use Nothing as the default value, provided this is not an expected value for the argument. Optional Parameters and Overloading Another way to define a procedure with optional parameters is to use overloading.