JS block scope


Block scope means that variables and functions belong not only to the scope in which they are located, but also to a block of code (usually inside {..})

for(var i=0;i<10;i++){

    var j = 12;

}

console.log(i,j)//10 12

When a variable is declared with var, no matter where it is written, it ends up in the outer scope.

function foo(){

     var a= 10;
}
console.log(a); // a is not defined



Related


What happens when using block scope variables for JS enclosing?

Billpg A while ago I asked a question using this sample JS code... for (var myindex = 0; myindex < mylist.length; myindex += 1) { var copyindex = myindex; MyAsync(mylist[myindex], function () { alert(copyindex); }); } (The answer is actually to call a

What happens when using block scope variables for JS closures?

Bilger A while ago I asked a question using this sample JS code... for (var myindex = 0; myindex < mylist.length; myindex += 1) { var copyindex = myindex; MyAsync(mylist[myindex], function () { alert(copyindex); }); } (The answer is actually to call a

What happens when using block scope variables for JS closures?

Bilger A while ago I asked a question using this sample JS code... for (var myindex = 0; myindex < mylist.length; myindex += 1) { var copyindex = myindex; MyAsync(mylist[myindex], function () { alert(copyindex); }); } (The answer is actually to call a

Block Scope, Function Scope and Local Scope in Javascript

3 Is block scope sometimes the same as function scope ? I know that function scoping applies to everything inside a function , but can't figure out exactly what block scoping is . For Javascript, is it currently recommended let/ constreplaced varfor future mai

Block Scope, Function Scope and Local Scope in Javascript

3 Is block scope sometimes the same as function scope ? I know that function scoping applies to everything inside a function , but can't figure out exactly what block scoping is . For Javascript, is it currently recommended let/ constreplaced varfor future mai

Block Scope, Function Scope and Local Scope in Javascript

3 Is block scope sometimes the same as function scope ? I know that function scoping applies to everything inside a function , but can't figure out exactly what block scoping is . For Javascript, is it currently recommended let/ constreplaced varfor future mai

Block Scope, Function Scope and Local Scope in Javascript

3 Is block scope sometimes the same as function scope ? I know that function scoping applies to everything inside a function , but can't figure out exactly what block scoping is . For Javascript, is it currently recommended let/ constreplaced varfor future mai

Block Scope, Function Scope and Local Scope in Javascript

3 Is block scope sometimes the same as function scope ? I know that function scoping applies to everything inside a function , but can't figure out exactly what block scoping is . For Javascript, is it currently recommended let/ constreplaced varfor future mai

Block scope in Python

Johan Råde: When writing code in other languages, a block scope is sometimes created like this: statement ... statement { statement ... statement } statement ... statement One of the (many) purposes is to improve the readability of the code: to sh

block scope variable

Paul: this will compile class X { public static void main(String args[]) { { int a = 2; } { int a = 3; } } } it won't class X { public static void main(String args[]) {

Proxy() block scope - Javascript

Herdev I'm having trouble using the Proxy() object in Javascript . This code works as expected when I pass in the target and there is no handler: const scope = new Proxy({a: 2, b: 2}, {}); with (scope) { a + b; } However, it doesn't work when I pass in a

block scope variable

Paul: this will compile class X { public static void main(String args[]) { { int a = 2; } { int a = 3; } } } it won't class X { public static void main(String args[]) {

Ruby - block scope

username I have a method that takes different actions depending on the situation, so I want to be able to pass a block to the method and it will execute if the block is given. However, I am confused about the scope of the variable in the block passed in. E.g:

Variable scope in block

Khan I'm learning Swift, and since there are compilers available now on Linux, I installed it and tested some programs. I don't understand one thing. Why does this contrived example get errors during compilation? var x = 86; if x <= 32 { ++x; print(x)

Block scope for let and for...of

stamp letStatements in ES2015 allow us to declare block-scoped variables, for example, the following code does what we want: let fs = []; for (let i = 0; i < 3; i++) { fs.push(() => i); } console.log(fs.map(f => f())); // 0, 1, 2 However, it doesn't seem

Block scope and internal linking?

p According to the C18 standard (6.7.9): If the declaration of an identifier has block scope , and the identifier has external or internal linkage , the declaration shall have no initializer for the identifier. I don't have any problem with block scope + exter

Block scope for let and for...of

stamp letStatements in ES2015 allow us to declare block-scoped variables, for example, the following code does what we want: let fs = []; for (let i = 0; i < 3; i++) { fs.push(() => i); } console.log(fs.map(f => f())); // 0, 1, 2 However, it doesn't seem

Proxy() block scope - Javascript

Herdev I'm having trouble using the Proxy() object in Javascript . This code works as expected when I pass in the target and there is no handler: const scope = new Proxy({a: 2, b: 2}, {}); with (scope) { a + b; } However, it doesn't work when I pass in a

Proxy() block scope - Javascript

Herdev I'm having trouble using the Proxy() object in Javascript . This code works as expected when I pass in the target and there is no handler: const scope = new Proxy({a: 2, b: 2}, {}); with (scope) { a + b; } However, it doesn't work when I pass in a

Proxy() block scope - Javascript

Herdev I'm having trouble using the Proxy() object in Javascript . This code works as expected when I pass in the target and there is no handler: const scope = new Proxy({a: 2, b: 2}, {}); with (scope) { a + b; } However, it doesn't work when I pass in a

C block scope

ARF I am trying to understand the meaning of block scope in C. I realize that identifiers defined in scope are not visible outside the scope, but what are the implications of doing block scoping at the instruction level? Does entering or exiting block scope im

Ruby - block scope

username I have a method that takes different actions depending on the situation, so I want to be able to pass a block to the method and it will execute if the block is given. However, I am confused about the scope of the variable in the block passed in. E.g:

Languages have block scope?

Phoenix I'm reading about function scope vs block scope. And learned that Javascript has functional scope. Now, when I think about it, all languages I know have function scope. I don't really know of any language that has block scope. Can you guys tell me some

Languages have block scope?

Phoenix I'm reading about function scope vs block scope. And learned that Javascript has functional scope. Now, when I think about it, all languages I know have function scope. I don't really know of any language that has block scope. Can you guys tell me some

Block scope and internal linking?

p According to the C18 standard (6.7.9): If the declaration of an identifier has block scope , and the identifier has external or internal linkage , the declaration shall have no initializer for the identifier. I don't have any problem with block scope + exter

block scope variable

Paul: this will compile class X { public static void main(String args[]) { { int a = 2; } { int a = 3; } } } it won't class X { public static void main(String args[]) {

Block scope in Python

Johan Råde: When writing code in other languages, a block scope is sometimes created like this: statement ... statement { statement ... statement } statement ... statement One of the (many) purposes is to improve the readability of the code: to sh

Block scope and internal linking?

p According to the C18 standard (6.7.9): If the declaration of an identifier has block scope , and the identifier has external or internal linkage , the declaration shall have no initializer for the identifier. I don't have any problem with block scope + exter

Block scope for let and for...of

stamp letStatements in ES2015 allow us to declare block-scoped variables, for example, the following code does what we want: let fs = []; for (let i = 0; i < 3; i++) { fs.push(() => i); } console.log(fs.map(f => f())); // 0, 1, 2 However, it doesn't seem