hoisting

Function Expression itself cannot assign Name to another Value

由 穿精又带淫゛_ 提交于 2019-12-05 16:20:12
In the code below: (function (){ function test(){};//"function" var test;//"undefined" var printTest = typeof test; document.write(printTest); })(); printTest will display "function" instead of "undefined", which makes sense since from my understanding, any variable declarations are always "hoisted" to the top of the execution context (which in this case is function execution context) This makes the function declaration "test()" to be the one that appears later in the current execution context. Now consider this code where I actually assign a value to var declaration "var test =1". (function (

Is there a purpose to hoisting variables?

由 廉价感情. 提交于 2019-12-04 08:15:39
I've been learning a lot of Javascript lately and I've been trying to understand the value (if there is any) of hoisting variables. I understand (now) that JS is a two pass system, it compiles and then executes. Also, I understand that the var keyword 'exists' in the lexical scope it was declared, hence why it's 'undefined' if it's called before it's assigned a value by the engine. The question is, why does that even matter? What use is there to hoisting variables that you can't do without hoisting? I feel like it just creates less-readable code with no gain ... is there an example(s) of where

JavaScript hoisting and scope

由 断了今生、忘了曾经 提交于 2019-12-04 06:41:39
问题 why the foo() function logs undefined ? The first text variable is a global variable so foo() should have an access to it. var text = "outside"; function foo() { console.log(text); var text = "inside"; } foo(); 回答1: Even though the var statement is after the console.log() statement, the declaration is hoisted to the beginning of the function. So this declares a local variable that shadows the global variable. But the initialization doesn't happen until you actually get to the statement, which

Function names defined as parameters to a function call aren't hoisted. Why not?

由 好久不见. 提交于 2019-12-04 03:37:23
问题 Consider the following code. <!DOCTYPE html> <script> console.log(a); function a() {} </script> Notice that a is seemingly accessed before it is defined. The console output is: (jsfiddle) function a() {} Function and variable names are defined before any other code runs, so the console.log call works here. This is called hoisting. But this doesn't work if the function is defined as a parameters in a function call. Look at this code. <!DOCTYPE html> <script> function a() {} a(function b() {});

Hoisting between different files

由 瘦欲@ 提交于 2019-12-02 11:24:02
问题 Is there a way to do functions and variable hoisting between source code present in different files? That is, something like //Inside firstfile.js foo === "bar" //should return true and //Inside secondfile.js function bar() { this.foo = "bar"; } I guess this is not possible, as different files as parsed and executed separately and in order by most javascript engines, but I do not know for sure. I don't know even if this is in the spec from ECMA, as the parsing of different files is not really

Bundling ES6 classes with Webpack. Is there a way to hoist extended classes?

由 天涯浪子 提交于 2019-12-02 08:30:36
问题 Can Webpack hoist extended classes? I am using Webpack and Babel to bundle and transpile a bunch of classes, each from a separate file. My Webpack entry file is an index.js file containing import statements of every class ordered by name, index.js: import classA from './a'; import classB from './b'; import classC from './c'; import classD from './d'; ... a.js: export class classA extends classD { constructor(...) { super(...); } } My problem is that the classes gets imported ordered by name,

JavaScript hoisting and scope

由 女生的网名这么多〃 提交于 2019-12-02 08:14:43
why the foo() function logs undefined ? The first text variable is a global variable so foo() should have an access to it. var text = "outside"; function foo() { console.log(text); var text = "inside"; } foo(); Even though the var statement is after the console.log() statement, the declaration is hoisted to the beginning of the function. So this declares a local variable that shadows the global variable. But the initialization doesn't happen until you actually get to the statement, which is after the console.log() statement. So your function is equivalent to: function foo() { var text; console

Can you clarify this JavaScript variable hoisting behavior?

由 走远了吗. 提交于 2019-12-02 06:58:52
问题 Case1: var text = 'outside'; function logIt(){ console.log(text); text ='inside'; } logIt(); //prints outside. why? I thought the text inside the function logIt() will be hoisted to the top of the function and will print undefined ? Case2: var text = 'outside'; function logIt(){ console.log(text); var text ='inside'; } logIt(); //prints undefined This one prints undefined as expected. Could someone explain why in case1 we getting the value outside ? 回答1: It's the variable declaration that's

JavaScript hoisting function vs function variable

由 一世执手 提交于 2019-12-02 05:32:24
问题 Here is my javascript code : console.log(a); c(); b(); var a = 'Hello World'; var b = function(){ console.log("B is called"); } function c(){ console.log("C is called"); } Now here is output : undefined hoisting.html:12 C is called hoisting.html:6 Uncaught TypeError: b is not a function My question is regarding why c() and b() behaving differently. And b should throw error something like b is not defined. 回答1: A Function Declaration will be hoisted along with its body. A Function Expression

Hoisting between different files

由 孤街醉人 提交于 2019-12-02 04:32:44
Is there a way to do functions and variable hoisting between source code present in different files? That is, something like //Inside firstfile.js foo === "bar" //should return true and //Inside secondfile.js function bar() { this.foo = "bar"; } I guess this is not possible, as different files as parsed and executed separately and in order by most javascript engines, but I do not know for sure. I don't know even if this is in the spec from ECMA, as the parsing of different files is not really part of the language. I originally thought this was a more interesting question than it actually
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