hoisting

JavaScript Inheritance and Hoisting

由 ☆樱花仙子☆ 提交于 2019-12-25 04:48:12
问题 In my current web project, I'm working with multiple JavaScript files, each containing type definitions that inherit from other types. So in any given file, I could have something like ... function Type(){ ParentType.call(this); } Type.prototype = Object.create( ParentType.prototype ); Type.prototype.constructor = Type; ... with the ParentType declared similarly in another file: function ParentType(){ this.data = ""; } Since working with many JavaScript files becomes bothersome in the <head>

Property added to a JS object as a prototype is hoisted, whereas a prototype function is not

由 梦想的初衷 提交于 2019-12-23 20:39:25
问题 I am (or at least I thought I was) pretty much familiar with the concept of Hoisting in JavaScript. Consider the following statements: A function declaration will be hoisted along with its body, whereas a function expression will not; only the var statement will be hoisted . “ Function declarations and function variables are always moved (‘hoisted’) to the top of their JavaScript scope by the JavaScript interpreter” - Berry Cherry Now consider the following function: function User() { this

Is a function hoisted if it is defined within an if condition?

由 做~自己de王妃 提交于 2019-12-22 05:06:22
问题 So suppose I have something like this var x = 1; if (function f(){}) { x += typeof f; } x; This outputs "1undefined". I thought it should have output "1function", because function f(){} should have been hoisted above the if. This is clearly not the case - why? I thought function declarations and bodies were always hoisted to the top of the scope? 回答1: Function declarations are hoisted. Function expressions are not. This creates a named function expression: if(function f(){}) It doesn't do

Confused about hoisting

由 别说谁变了你拦得住时间么 提交于 2019-12-20 02:38:56
问题 consider these slightly two different versions of hoisting... mylocation = "dublin" function outputPosition() { alert(mylocation); mylocation = "fingal" ; alert(mylocation); } outputPosition(); This will output "fingal" and then "fingal" mylocation = "dublin" function outputPosition() { alert(mylocation); var mylocation = "fingal" ; alert(mylocation); } outputPosition(); This will output "undefined" and "fingal" Why? 回答1: Once you declare variable using var keyword within a javascript

Why is no ReferenceError being thrown if a variable is used before it’s declared?

由 左心房为你撑大大i 提交于 2019-12-17 19:52:49
问题 I’m trying to wrap my head around the behavior of reference errors thrown in JavaScript. In the following example, a ReferenceError is thrown at the second line, and execution breaks: var obj = {}; obj.func1 = func2; alert('Completed'); Whereas in this example, the code completes successfully, though obj.func1 remains undefined : var obj = {}; obj.func1 = func2; var func2 = function() { alert('func2'); }; alert('Completed'); My assumption was that an error would be thrown at the second line

Why is my JavaScript hoisted local variable returning undefined but the hoisted global variable is returning blank? [duplicate]

由 梦想的初衷 提交于 2019-12-17 14:44:28
问题 This question already has answers here : Why do I get the value “result” for this closure? (3 answers) Closed 4 years ago . As part of my learning JavaScript, I try to write code to demonstrate the concept I am learning; today I'm learning hoisted variables. Here is the code I wrote: console.log("A: My name is " + name); function happy() { console.log ("1: I am " + feeling); var feeling = "happy"; console.log ("2: I am " + feeling); } happy(); var name = "Jim"; console.log("B: My name is " +

Why do catch clauses have their own lexical environment?

由 不问归期 提交于 2019-12-17 06:51:35
问题 Consider the following excerpt from ECMA-262 v5.1 (which I recently saw in this question): A Lexical Environment is a specification type used to define the association of Identifiers to specific variables and functions based upon the lexical nesting structure of ECMAScript code. A Lexical Environment consists of an Environment Record and a possibly null reference to an outer Lexical Environment. Usually a Lexical Environment is associated with some specific syntactic structure of ECMAScript

JavaScript 'hoisting' [duplicate]

由 孤街醉人 提交于 2019-12-17 01:39:49
问题 This question already has answers here : Javascript function scoping and hoisting (16 answers) Closed 4 years ago . I came across JavaScript 'hoisting' and I didn't figure out how this snippet of code really functions: var a = 1; function b() { a = 10; return; function a() {} } b(); alert(a); I know that function declaration like ( function a() {} ) is going to be hoisted to the top of the function b scope but it should not override the value of a (because function declarations override

Does JavaScript hoist if statements when object literals are involved?

由 感情迁移 提交于 2019-12-13 09:53:26
问题 var foo = {}; document.body.innerHTML = console.log = location.hash = 'Hi ' + '<br> ' + foo.bar + '<br> ' + foo.baz; setTimeout(function() { foo.baz = foo["bar"] = []; foo.bar.push(new Date); foo.baz.push(new Date); document.body.innerHTML = console.log = location.hash = 'Hi ' + '<br> ' + foo.bar + '<br> ' + foo.baz}, 5000); 回答1: Since you set node.bar equal to false , (node.foo && node.bar) will evaluate to false whether the properties are attached or not. Rather than checking if those

does this variable get hoisted no matter what?

由 回眸只為那壹抹淺笑 提交于 2019-12-13 05:51:26
问题 Does var foo get hoisted to the top of the stack even when the code inside the false block isn't ever going to be executed? function foo(){ if ( false ) { var foo = 'bar'; //will this be hoisted even if its never executed? } } I'm seeing that it is and was just confused...I didn't expect it to get hoisted in its wrapped in a false condition. 回答1: Yes; the hoisting happens before the code is run, so whether or not the if statement comes out true or false isn't yet known. 来源： https:/
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