This article mainly introduces ordinary functions, anonymous functions, and closure functions
1. Introduction to common functions
1.1 Example
1.2 Overwriting of functions with the same name in Js
In JS, functions are not overloaded. If you define functions with the same function name and different parameter signatures, the later functions will overwrite the previous functions. When called, only the following functions will be called.
1.3 arguments object
arguments is similar to C#'s params, operating variable parameters: the number of parameters passed into the function is greater than the number of parameters when defined.
1.4 Default range value of function
If the function does not specify a return value, the default return value is 'undefined'
2. Anonymous function
2.1 Variable anonymous function
2.1.1 Description
Functions can be assigned to variables and events.
2.1.2 Example
2.1.3 Applicable Scenarios
①Avoid function name pollution. If you first declare a function with a name and then assign it to a variable or event, you will abuse the function name.
2.2 Nameless anonymous function
2.2.1 Description
That is, when the function is declared, it is followed by the parameters. When JS syntax parses this function, the code inside is executed immediately.
2.2.2 Example
2.2.3 Applicable Scenarios
①It only needs to be executed once. If the browser is loaded, the function only needs to be executed once and will not be executed later.
3. Closure function
3.1 Description
Assume that function A declares a function B inside, function B refers to a variable outside function B, and the return value of function A is a reference to function B. Then function B is a closure function.
3.2 Example
3.2.1 Example 1: Global reference and local reference
allShowA is a global variable that references function funA. Repeatedly running allShowA() will output the accumulated values of 1, 2, 3, 4, etc.
Execute the function partShowA(), because only the local variable showa is declared internally to reference funA. After execution, due to the scope, the resources occupied by showa are released.
The key to closure is scope: the resources occupied by global variables will only be released when the page changes or the browser is closed. When var allShowA = funA(), it is equivalent to allShowA referencing funB(), so that the resources in funB() will not be recycled by GC, so the resources in funA() will not be recycled either.
3.2.2 Example 2: Parametric closure function
3.2.3 Example 3: Variable sharing within parent function funA
3.3 Applicable Scenarios
① Ensure the safety of the variables inside the function funA, because the variables of funA cannot be directly accessed from the outside.
Have you guys learned anything about the JavaScript function? If you have any questions, please leave me a message.