What is the code of custom function method in javascript

In JavaScript, the code of a custom function method is "function method name (parameter list) {method body}"; JavaScript functions need to be defined using lowercase function, and there is no need to use "var" in the parameter list ", otherwise an error will be reported.

The operating environment of this tutorial: Windows 10 system, JavaScript version 1.8.5, Dell G3 computer.

What is the code of custom function method in javascript

JS custom function/method

Brief description and function of function

If the code needs to be repeated Therefore, in order to uniformly write and use it, it can be encapsulated in a function/method;

Function: enhance the reusability of the code;

Function format

function 方法名(参数列表)
{
方法体
}

Note:

js function definition must use function, and must be in lowercase;

js function does not need to define the return value type, just write it directly after function;

There is no need to use the var keyword in the parameter list in the JS defined function, otherwise an error will be reported;

js function weight, return does not need to be written, or a specific value can be returned, or a more recent return can be used;

There must be a return value after the function call is executed. The type of the return value is determined by return. If no specific value is returned in the function, undefined will be returned by default.

Example:

function getSum(a,b)         //Sum:z综合;
{
return a+b;
}

js There is no function overloading. If the function has the same name, only the methods overwrite each other, and the last defined function overwrites the previous definition.

Because there is no function overloading in js, the function is only called based on the method name in js, even if it is actually If the formal parameters of the participating functions do not match, it will not affect normal use;

If the formal parameters are not assigned a value, the default value passed in is undefined

For example:

 <script>
        function getNum(a,b)//不需要var
        {
            return a+b;
        }
        function getNum(a,b,c)
        {
            return a+b+c;
        }
        alert(getNum(1,2));
        //得出结果为NaN,因为没有第三个参数值的出现,所以a+b+c没有正确的值;
        
    </script>

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