Set function parameter default value in js

Set function parameter default value in js

When div + css simulates the js information box class library, a problem occurs. When no parameter is passed, the prompt information is automatically used as the window title. The specific implementation is as follows:

Today, I encountered a problem when I wrote a class library for div + css to simulate js information boxes. I want to automatically use "prompt information" as the window title when I didn't pass the parameter. I tried to write it like this.

The Code is as follows:

Function MessageBox (title = ""){

}

 

No doubt I failed to run (or I will not post this blog post)

 

Finally, Baidu found such a good thing.

The Code is as follows:

Function test (){

Var B = arguments [0]? Arguments [0]: 50;

Return a + ':' + B;

}

 

According to my understanding, arguments is probably something similar to an array. The subscript starts from 0 and represents the parameters of this function in sequence.

 

For example, in the previous example, arguments [0] indicates parameter.

 

Actually arguments [0]? Arguments [0]: 50 can also be written as: arguments [0] | 50; the writing method is quite simplified. The above is the method for setting the default value of the function parameter in js.