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anonymous123
5,794 PointsLocal Scope (JavaScript)
The article im reading which was shared by Mr. McFarland from TeamTreeHouse in the teachers notes of a JS lesson says that the local scope and function scope are different but from what Ive read local scope is just another word for function scope. (I dont like reading anything that doesnt come from a reliable source such as the MDN so for me there isnt a lot of information about Local Scope at least for me.) Can anyone that learned about local scope from a reliable source explain local scope to me?
anonymous123
5,794 PointsDave StSomeWhere -------- Local Scope A local scope refers to any scope defined past the global scope. There is typically one global scope, and each function defined has its own (nested) local scope. Any function defined within another function has a local scope which is linked to the outer function.
If I define a function and create variables inside it, those variables becomes locally scoped. Take this example:
// Scope A: Global scope out here var myFunction = function () { // Scope B: Local scope in here }; Any locally scoped items are not visible in the global scope - unless exposed, meaning if I define functions or variables within a new scope, it’s inaccessible outside of that current scope. A simple example of this is the following:
var myFunction = function () { var name = 'Todd'; console.log(name); // Todd }; // Uncaught ReferenceError: name is not defined console.log(name); The variable name is scoped locally, it isn’t exposed to the parent scope and therefore undefined.
-----Function scope All scopes in JavaScript are created with Function Scope only, they aren’t created by for or while loops or expression statements like if or switch. New functions = new scope - that’s the rule. A simple example to demonstrate this scope creation:
// Scope A var myFunction = function () { // Scope B var myOtherFunction = function () { // Scope C }; }; It’s easy to create new scope and create local variables/functions/objects.
2 Answers
Liam Clarke
19,938 PointsHello
local scope is more of a general term used as it means the scope is local to whatever that case. the following are local scopes:
Module scope
//console.js
const localExample = 'local example works';
module.exports.moduleExample = 'module example works';
//app.js
const moduleTest = require('./console');
console.log(`local variable ${moduleTest.localExample}`);
console.log(`module variable ${moduleTest.moduleExample}`);
//output
local variable undefined
module variable module example works
This is due to the localExample only being local to that module and therefore in the local scope.
Function scope
//app.js
const globalScope = 'global scope example works';
function functionExample() {
const localExample = 'local scope example works';
}
console.log(`The ${globalScope}`);
console.log(`The ${localExample}`);
//output
The global scope example works
ReferenceError: localExample is not defined
The localExample is only set within the brackets of the function and therefore making it local scope.
Block scope
Block scope is pretty much the same as function scope but is local to any block, that mean objects literals, functions, conditionals, etc
Something worth mentioning, let and const are both block scoped, unlike var so they should be declared at the top of each block.
This will not work:
(function () {
console.log(blockTest);
const blockTest = 'The is a block scope test.';
})();
martinjones1
Front End Web Development Techdegree Graduate 44,824 PointsIf you want to find out more about scope in-depth, I would recommend the YDKJS series from Kyle Simpson.
It is available for free online on GitHub.
https://github.com/getify/You-Dont-Know-JS/blob/master/scope%20%26%20closures/ch1.md
TL;DR section
https://github.com/getify/You-Dont-Know-JS/blob/master/scope%20%26%20closures/ch1.md#review-tldr
Dave StSomeWhere
19,870 PointsDave StSomeWhere
19,870 PointsPlease share the conflicting details. FYI here's the MDN Local Scope definition