don t know js scope closures

distributed systems.This may be self-evident or may be surprising-depending on your ability to digest all languages, but although JS is a generic category of dynamic and interpretive languages, it is actually a compiled language. It is not compiled in advance because there are many traditional compiler languages that are not the product of a variety of distributed compilation systems.But, nevertheless, the JavaScript engine performs many of the same

(function Timeouthandler () {...}, 1000);Block scope:The Let keyword binds a variable to any scope in which it resides;Claims made with let are not promoted in the block scope;Improve:Only the declaration itself will be promoted, and the assignment or other running logic will remain in place.If the promotion changes the order of code execution, it can cause very serious damage;Both the function declaration

; function Baz () { // 2 } Bar (baz);} function Bar (FN) { // closures }var fn; function foo () { var a = 2; function Baz () { console.log (a); } = baz ();} function Bar () { // closed package }foo (); bar ();The internal function timer is passed to the Settimeout,timer that covers the wait scope, so a reference to the message is retained. After wait executes 1

we fix it? We want the timer to capture a copy of I for Each loop, but according to the principle of the scope, the reality is that although the 5 functions of the loop are defined separately in each iteration, they are enclosed in a shared global scope, so there is actually only one I, and all functions share an I The reference. If the callback of the deferred function is defined 5 times, and the loop is

other asynchronous (or synchronous) task , As long as the callback function is used, you are actually using closures!3) Loops and closures for (var i = 1; I ) { setTimeout (function timer () { Console.log ( i); * +);}Each time the print will be 6, the callback of the deferred function will be executed at the end of the loop, viewing the source code .Depending on how the

JavaScript scope closure (JavaScript you Don't know) JavaScript closure is a deep understanding of JavaScript development engineers. In March, I wrote my blog "JavaScript closure", which briefly described the working process of the closure and provided several examples. I didn't figure it out!Now with a more in-depth understanding of JavaScript, I have just read 《 JavaScript that you don't

You don't know. JavaScript (roll up) This book seems to me to be a good book, the book in a relatively concise language to describe the JS of those "pits", here to write some blog record notes for digestion and absorption.1 Compilation PrincipleIn this book, the beginning of the proposed: JavaScript is a compiler language, I started to think this is a domestic translation of the pot, translation is not accu

Closed PackageClosed Packagefunction objects can be associated with each other through the scope chain, and variables inside the function body can be stored within the scope of the function.This feature is called "closures".What is a variable?A variable is a name assigned to all things ;the function of Var, initializes the variable. Variable scopeThe area where t

(b.test);Note:① the definition of Javascript from other websitesMozilla.org:JavaScript is a lightweight, interpreted, object-oriented scripting language ... It is a prototype-based, multi-paradigm dynamic scripting language.Baidu Encyclopedia: JavaScript a literal translation script language, is a dynamic type, weak type, prototype-based language, built-in support type. Its interpreter is called the JavaScript engine and is part of the browser.Reference: Nanyi "Javascript Strict mode detailed"M

-angle, but has failed! get long time, just solve the problem. The process of solving is actually very wonderful, when I see the mybatis XML inside the think, why did you get long time to solve the problem? or oneself JS This together of knowledge is deficient ah. Below, put out the code, give everyone a tan: $ (function () {$ ("form:input.required"). each (function () {var $required = $ (" As above code:

to the engine, provided that the program is running in a non-strict mode.Next, if the RHS query finds a variable, but you try to make an unreasonable operation on the variable, such as trying to make a function call to a value of a non-function type, or referencing a property in a value of null or undefined type, the engine throws another type exception, It's called TypeError.Referenceerror is related to the discriminant failure of the same scope, wh

Closures mainly involve several other features of JS: Scope chain, garbage (memory) recycling mechanism, function nesting, and so on.Scope Chain: The function is created at the time of definition, used to find an index of the value of the variable used, and his internal rule is to put the local variables of the function itself in the first place, put the variable