JavaScript Basics -5 JavaScript functions

First, JavaScript function definition

Functions (methods, procedures)

-Functions (function), sometimes called methods, or processes (Procedure)

-a block of code that is predefined and can be reused, which can contain multiple executable statements

-function is essentially a fully functional object

Functions that define functions (methods, procedures)

-Define a function using the keyword function

-Definition rules and identifiers for function names are always, case sensitive

-The simplest function definition

650) this.width=650; "src=" Http://s3.51cto.com/wyfs02/M00/7E/00/wKioL1b05HvwsUhiAAC98SfUbko836.png "title=" Web.png "alt=" Wkiol1b05hvwsuhiaac98sfubko836.png "/>

Defining parameters and return values

-A slightly more complex function may need to declare the execution parameters

-or use the RETURN keyword to declare the return value of the function

650) this.width=650; "src=" Http://s5.51cto.com/wyfs02/M00/7E/03/wKiom1b047ngJkxHAAG0wYapA3M162.png "title=" Web.png "alt=" Wkiom1b047ngjkxhaag0wyapa3m162.png "/>

Second, the invocation of JavaScript functions

Parameter passing when calling a function

-If the function definition specifies that parameters need to be passed, the required value must be provided when calling this function.

The following functions are defined:

650) this.width=650; "src=" Http://s1.51cto.com/wyfs02/M00/7E/00/wKioL1b05PSCtbzMAABjze6aTzM882.png "title=" Web.png "alt=" Wkiol1b05psctbzmaabjze6atzm882.png "/>

650) this.width=650; "src=" Http://s4.51cto.com/wyfs02/M01/7E/04/wKiom1b05IThzPrGAAFK5B6vHNs040.png "title=" Web.png "alt=" Wkiom1b05ithzprgaafk5b6vhns040.png "/>

Get return value

-If the return value is declared in the function definition, you can receive this return value when the function is called.

The following functions are defined:

650) this.width=650; "src=" Http://s5.51cto.com/wyfs02/M00/7E/00/wKioL1b05n2htlu5AABCWTZl_Ck531.png "title=" Web.png "alt=" Wkiol1b05n2htlu5aabcwtzl_ck531.png "/>

650) this.width=650; "src=" Http://s5.51cto.com/wyfs02/M01/7E/04/wKiom1b05gXRTKvqAADEDMw5rO4774.png "title=" Web.png "alt=" Wkiom1b05gxrtkvqaadedmw5ro4774.png "/>

function called inside function

-You can call other functions in a function body

650) this.width=650; "src=" Http://s2.51cto.com/wyfs02/M00/7E/00/wKioL1b05xTwWqUSAADKy5IR5k0666.png "title=" Web.png "alt=" Wkiol1b05xtwwqusaadky5ir5k0666.png "/>

-complex example of calling other functions in the function body

650) this.width=650; "src=" Http://s1.51cto.com/wyfs02/M00/7E/04/wKiom1b05vzQptzmAAFIWXglQKc118.png "title=" Web.png "alt=" Wkiom1b05vzqptzmaafiwxglqkc118.png "/>

Iii. Scope of JavaScript variables

Scope overview

-scope is the accessible range of variables and functions, he controls the visibility and life cycle of variables and functions

-In JavaScript, the scope of variables and functions is divided into:

-function scope, accessible only within the current function

-Global scope, once defined, can be accessed anywhere in the code

Variables in the scope of a function

-In the function scope, the German variable (local variable) is accessible only within the current function and cannot be accessed from this range.

650) this.width=650; "src=" Http://s5.51cto.com/wyfs02/M02/7E/01/wKioL1b07FyQJ9OSAACoZjZRA3Y585.png "title=" Web.png "alt=" Wkiol1b07fyqj9osaacozjzra3y585.png "/>

Variables in a global scope

-Variables (global variables) in the global scope can be accessed anywhere in the code

-variables defined at the outermost layer are global variables

650) this.width=650; "src=" Http://s1.51cto.com/wyfs02/M02/7E/01/wKioL1b07TqhK06SAAHBazscjFc355.png "title=" Web.png "alt=" Wkiol1b07tqhk06saahbazscjfc355.png "/>

Declaration in advance

-the JavaScript program reads all VAR-declared variables and function-declared functions to the top of all scopes before it is formally executed

-but the assignment of the variable is kept in the original position and executed with the script interpretation.

such as

650) this.width=650; "src=" Http://s4.51cto.com/wyfs02/M02/7E/05/wKiom1b077Sxt5kmAAFBOyOhae0150.png "title=" Web.png "alt=" Wkiom1b077sxt5kmaafboyohae0150.png "/>

-the declaration can be advanced only to the top of the scope in advance

650) this.width=650; "src=" Http://s1.51cto.com/wyfs02/M00/7E/05/wKiom1b08DXRNkXRAACwQcUKDRg437.png "title=" Web.png "alt=" Wkiom1b08dxrnkxraacwqcukdrg437.png "/>

is equivalent to:

650) this.width=650; "src=" Http://s5.51cto.com/wyfs02/M01/7E/01/wKioL1b08PexFaknAADZDBTQtaY905.png "title=" Web.png "alt=" Wkiol1b08pexfaknaadzdbtqtay905.png "/>

-declaration not only advance the variable declaration, but also advance the function declaration

650) this.width=650; "src=" Http://s3.51cto.com/wyfs02/M01/7E/01/wKioL1b09DOQcVxRAABLoCbpbWI635.png "title=" Web.png "alt=" Wkiol1b09doqcvxraablocbpbwi635.png "/>

is equivalent to:

650) this.width=650; "src=" Http://s1.51cto.com/wyfs02/M02/7E/05/wKiom1b087aBkoPkAABMb2V7HpM853.png "title=" Web.png "alt=" Wkiom1b087abkopkaabmb2v7hpm853.png "/>

-Summary: The declaration of Variables and the declaration of functions should be centered at the top of the current scope as much as possible.

Pass by value

-Passing by value means copying the value of an argument variable to the shape of a method parametric

-When you pass a parameter to a method in JavaScript, it is passed by value

-If the raw type data is passed, the value of the parameter variable is modified within the method without affecting the external real parametric

such as

650) this.width=650; "src=" Http://s3.51cto.com/wyfs02/M00/7E/02/wKioL1b09i_iL19qAAFOvcrhOJU379.png "title=" Web.png "alt=" Wkiol1b09i_il19qaafovcrhoju379.png "/>

Scope of the function

-Similar to variables, the scope of the function is also divided into "global scope (global function)" and "function scope (local function)"

-the function defined at the outermost layer is the global function

650) this.width=650; "src=" Http://s2.51cto.com/wyfs02/M01/7E/05/wKiom1b09svQTu0yAAB_pgoRDss188.png "title=" Web.png "alt=" Wkiom1b09svqtu0yaab_pgordss188.png "/>

-Functions defined inside a function are local functions

650) this.width=650; "src=" Http://s3.51cto.com/wyfs02/M00/7E/02/wKioL1b097SDTOw5AAC_DiOasuo406.png "title=" Web.png "alt=" Wkiol1b097sdtow5aac_dioasuo406.png "/>

Third, JavaScript global functions

Overview of global functions

-a set of global functions is pre-defined in ECMAScript for users to use directly

650) this.width=650; "src=" Http://s3.51cto.com/wyfs02/M01/7E/02/wKioL1b0-y_SJ99FAAO3XQzkLBQ852.png "title=" Web.png "alt=" Wkiol1b0-y_sj99faao3xqzklbq852.png "/>

encodeURI and decodeURI

-The encodeURI () function is used to encode a Uniform Resource Identifier (URI), returning the encoded URI string

-The decodeURI () function is used to encode a string after encoding with encodeURI ()

650) this.width=650; "src=" Http://s1.51cto.com/wyfs02/M01/7E/02/wKioL1b0_Dvx1OD2AAFMbkGEUzk198.png "title=" Web.png "alt=" Wkiol1b0_dvx1od2aafmbkgeuzk198.png "/>

eval function

-The Eval () function is used to execute JavaScript code that appears as a string

-Use this function to enable JS to execute dynamic JavaScript source code

650) this.width=650; "src=" Http://s3.51cto.com/wyfs02/M00/7E/06/wKiom1b0_FSDR94NAAED3sjDpYQ738.png "title=" Web.png "alt=" Wkiom1b0_fsdr94naaed3sjdpyq738.png "/>

Summary: This chapter mainly introduces the JavaScript function

This article from the "Technical Exchange" blog, declined reprint!

JavaScript Basics -5 JavaScript functions