node. js Preliminary Understanding (3)--MU class network (callback, scope, context)

1.

1 //callback: Callback is the most basic method of asynchronous programming, node. JS needs to execute asynchronous logic in order, usually in the way of subsequent passing, the subsequent logic is encapsulated in the callback function, as the parameters of the starting function. 2 //named function3 functionLearn (something) {4 Console.log (something);5 }6 7 functionWe (callback,something) {8something+= ' is cool ';9 callback (something);Ten  One } A  -We (Learn, "Nodejs"); -  the //Anonymous Functions -Wefunction(something) { - Console.log (something) -}, ' linshuling ') +  -  + //sequential execution, two sequential executions, can get the results we want.  A varC=0; at functionPrintIt () { - Console.log (c); - } - functionPlus () { -C+=1; - } in  - Plus (); toPrintIt ();//1 +  -  the //because the plus function defers execution, the result is different and you can use a callback function to resolve the problem.  * varC=0; $ functionPrintIt () {Panax Notoginseng Console.log (c); - } the functionPlus () { +SetTimeout (function(){ AC+=1; the},1000); +      - } $  $ Plus (); -PrintIt ();//0 -  the  - //callback functionWuyi varC=0; the functionPrintIt () { - Console.log (c); Wu } - functionPlus (callback) { AboutSetTimeout (function(){ $C+=1; - callback (); -},1000); -      A } +  thePlus (printit);//1

2.

1 //variable scope: relates to the ability to invoke a function and access a variable. 2 varGlobalv= "This is global var";3 functionglobalf () {4     varLocalv= "This is local var";5 6Console.log (' Visis global/local var ');7Console.log (GLOBALV);//This is global var8Console.log (LOCALV);//This is local var9 TenGlobalv= "This is changed Globalv"; OneConsole.log (GLOBALV);//This is changed Globalv A  -     functionlocalf () { -         varInnerlv= "This is inner local var"; the  -Console.log ("Visis globalv/localv/innerlv var"); -Console.log (GLOBALV);//This is changed Globalv -Console.log (LOCALV);//This is local var +Console.log (INNERLV);//This is inner local var -     } + localf (); A  at } -Globalf ();

3.

1 //context: In JavaScript, this usually refers to the owner of the current function, and the owner is called the execution context. This is a keyword of javascript that represents an internal object that is automatically generated when the function is run. 2 //13 varpet={4Words: ' ... ',5Speakfunction(){6Console.log ( This. words);//...7Console.log ( This===pet);//true8 9     }Ten } One pet.speak (); A  -  - //2 the functionPet (words) { -      This. words=words; -Console.log ( This. words); -Console.log ( This);//the point is global +Console.log ( This===global);//true - } +Pet (' ... '); A  at //3 - functionPet (words) { -      This. words=words; -      This. speak=function(){ -Console.log ( This. words); -Console.log ( This); in     } - } to  + varcat=NewPet (' Miao '); -Cat.speak ();

4.

1 //Call and apply2 varpet={3Words: ' ... ',4Speakfunction(say) {5Console.log (say+ "+ This. words);6     }7 }8 //Pet.speak ("speak");9 Ten vardog={ OneWords: "Wang" A } -Pet.speak.call (dog, ' speak ');//change the execution context by call, point the Pet.speak this to the dog, followed by the arguments passed to the method.  - //Speak Wang the  -  -  -  +  - functionPet (words) { +      This. words=words; A      This. speak=function(say) { atConsole.log ( This. words); -     } - } - functionDog (words) { -Pet.call ( This, words); -     //pet.apply (this,arguments) in } -  to vardog=NewDog (' Wang '); +  -Dog.speak ();//Wang

node. js Preliminary Understanding (3)--MU class network (callback, scope, context)