JavaScript study notes (4) function function part_basic knowledge

A function is an event-driven or reusable block of code that executes when it is called.
Jscript supports two types of functions: one is the internal function of the language (such as eval()), and the other is created by yourself.

A variable declared inside a JavaScript function (using var) is a local variable, so it can only be accessed inside the function. (The scope of this variable is local).

You can use local variables with the same name in different functions because only the function in which the variable is declared will recognize the variable.

How to call functions

1. Ordinary call: functionName (actual parameters...)

2. Call through a variable pointing to the function:

var myVar = function name;

myVar(actual parameter...);

Function that returns a function

　1. When a function has no clear return value, the returned value is "undefined".

　2. When a function has a return value, whatever the return value is is returned.

We can return a function to the place where it was called by using the return statement.

When using the return statement, the function stops execution and returns the specified value.

Functions usually return a unique value, so this value may also be another function:

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Here, we just assign the return value to a variable and then call it like a normal function:

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If you want the returned function to be executed immediately, you can also use box()() to execute this code.

The parameters of all ECMAScript functions are passed by value, which means that the parameters are not passed by reference.

PS: If there is pass by reference, then the variable in the function will be a global variable and can also be accessed externally.

(1) Value type: numeric value, Boolean value, null, undefined.
(2) Reference type: object, array, function.

Reference type value: refers to those objects stored in heap memory, which means that what is saved in the variable is actually just a pointer. This pointer executes another location in the memory, and the object is saved at that location;
Create anonymous function

Copy code The code is as follows:

function(){
return ‘Lee’; //A separate anonymous function cannot be run. Even if it can be run, it cannot be called because it has no name
}

This kind of anonymous function has many uses in JQuery. Declare an anonymous function directly and use it immediately. The advantage of using anonymous functions is that you don't have to define a function that is used once and then don't use it, and it also avoids the problem of naming conflicts. There is no concept of namespace in js, so it is easy for function names to conflict. In the event of a naming conflict, the last declared one shall prevail.

Execute an anonymous function via self-execution:

Copy code The code is as follows:

//Execute anonymous function by self-execution

Assign the return value of the anonymous function's self-execution to a variable:

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//Assign the return value of the anonymous function's self-execution to the variable

Passing parameters to self-executing anonymous function:

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//Pass parameters of self-executing anonymous function

javascript creates dynamic function:

JavaScript supports the creation of dynamic functions. Dynamic functions must be defined using Function objects (Function is an object in JavaScript and is fixed. It is stipulated that the "F" of the Function object must be capitalized. When it is a function, we know It is a keyword used when defining a function: function funName(x, y). When it is Function (when F is capitalized), we know it is an object in JavaScript)

The basic format for creating a dynamic function: var variable name = new Function("Parameter 1", "Parameter 2", "Parameter n", "Execution statement");

Look at the following piece of code:

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