Please explain automatically global in javascript
I cannot understand the idea behind automatically global. I am reading the following:
https://www.w3schools.com/js/js_scope.asp
https://www.w3schools.com/js/tryit.asp?filename=tryjs_local_global
The function myFunction() is called. if I remove this call it displays nothing. I can't understand why the call to myFunction() is necessary for the undeclared variable in myFunction() to be automatically global. Seems not so intuitive.
javascript
asked Nov 16 '18 at 2:32
lilredindylilredindy
167
add a comment |
I cannot understand the idea behind automatically global. I am reading the following:
https://www.w3schools.com/js/js_scope.asp
https://www.w3schools.com/js/tryit.asp?filename=tryjs_local_global
The function myFunction() is called. if I remove this call it displays nothing. I can't understand why the call to myFunction() is necessary for the undeclared variable in myFunction() to be automatically global. Seems not so intuitive.
javascript
asked Nov 16 '18 at 2:32
lilredindylilredindy
167
Possible duplicate of What is the scope of variables in JavaScript?
– Abana Clara
Nov 16 '18 at 2:39
add a comment |
I cannot understand the idea behind automatically global. I am reading the following:
https://www.w3schools.com/js/js_scope.asp
https://www.w3schools.com/js/tryit.asp?filename=tryjs_local_global
The function myFunction() is called. if I remove this call it displays nothing. I can't understand why the call to myFunction() is necessary for the undeclared variable in myFunction() to be automatically global. Seems not so intuitive.
javascript
asked Nov 16 '18 at 2:32
lilredindylilredindy
167
I cannot understand the idea behind automatically global. I am reading the following:
https://www.w3schools.com/js/js_scope.asp
https://www.w3schools.com/js/tryit.asp?filename=tryjs_local_global
The function myFunction() is called. if I remove this call it displays nothing. I can't understand why the call to myFunction() is necessary for the undeclared variable in myFunction() to be automatically global. Seems not so intuitive.
javascript
javascript
asked Nov 16 '18 at 2:32
lilredindylilredindy
167
asked Nov 16 '18 at 2:32
lilredindylilredindy
167
edited Nov 16 '18 at 2:48
lilredindy
asked Nov 16 '18 at 2:32
lilredindylilredindy
167
asked Nov 16 '18 at 2:32
lilredindylilredindy
167
asked Nov 16 '18 at 2:32
lilredindylilredindy
167
167
Possible duplicate of What is the scope of variables in JavaScript?
– Abana Clara
Nov 16 '18 at 2:39
add a comment |
Possible duplicate of What is the scope of variables in JavaScript?
– Abana Clara
Nov 16 '18 at 2:39
Possible duplicate of What is the scope of variables in JavaScript?
– Abana Clara
Nov 16 '18 at 2:39
Possible duplicate of What is the scope of variables in JavaScript?
– Abana Clara
Nov 16 '18 at 2:39
add a comment |
3 Answers
3
active
oldest
votes
All it means is in this code:
function myFunction() {
carName = "Volvo";
}
carName exists outside myFunction after its execution, and is usable by other code. Whereas:
function myFunction() {
var carName = "Volvo";
}
carName only exists within myFunction, even after it's called. Code outside myFunction can't see it.
answered Nov 16 '18 at 2:35
ceejayozceejayoz
141k34215300
oh i see, it needs to be EXECUTED first...hmm i guess that would make sense
– lilredindy
Nov 16 '18 at 2:39
Right, if you never runmyFunction,carNamedoesn't ever exist, in any scope.
– ceejayoz
Nov 16 '18 at 2:41
add a comment |
expression
var varName = 'value';
declares variable with var varName and then assign a value 'value' to it with = 'value'
expression
varName = 'value';
just making the assignment a value 'value' to a variable 'varName' which should be declared previously
so
function a() {
var varName = 'a'
}
declare the variable varName locally and initiate it with 'a'
but
function b() {
varName = 'b'
}
just assigns the variable varName with the value 'b'. but the variable varName is to be declare in the paren global scope.
answered Nov 16 '18 at 2:46
hypp ersterhypp erster
212
add a comment |
When you 'declare' a variable with no explicit declaration keyword (var/let/const), then there is some ambiguity as to whether your intention was to reference an existing variable that may or may not be in a higher scope or to declare a new variable. Much of JavaScript's early defining behavior was to try to have fallback behavior for flexibility. When a variable is assigned to but there is no existing reference, it falls back to creating a variable. And without any declaration keyword there is no way to infer where your intended scope is, so it creates it in a global scope so that other possible references might find it.
In your case, when you call the function it references some variable. JavaScript doesn't know if this was meant to already exist or not, so it creates it in the global scope. As a result, it is still within scope and referenceable after the method is called.
answered Nov 16 '18 at 2:43
msg45fmsg45f
333613
add a comment |
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3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
All it means is in this code:
function myFunction() {
carName = "Volvo";
}
carName exists outside myFunction after its execution, and is usable by other code. Whereas:
function myFunction() {
var carName = "Volvo";
}
carName only exists within myFunction, even after it's called. Code outside myFunction can't see it.
answered Nov 16 '18 at 2:35
ceejayozceejayoz
141k34215300
oh i see, it needs to be EXECUTED first...hmm i guess that would make sense
– lilredindy
Nov 16 '18 at 2:39
Right, if you never runmyFunction,carNamedoesn't ever exist, in any scope.
– ceejayoz
Nov 16 '18 at 2:41
add a comment |
All it means is in this code:
function myFunction() {
carName = "Volvo";
}
carName exists outside myFunction after its execution, and is usable by other code. Whereas:
function myFunction() {
var carName = "Volvo";
}
carName only exists within myFunction, even after it's called. Code outside myFunction can't see it.
answered Nov 16 '18 at 2:35
ceejayozceejayoz
141k34215300
oh i see, it needs to be EXECUTED first...hmm i guess that would make sense
– lilredindy
Nov 16 '18 at 2:39
Right, if you never runmyFunction,carNamedoesn't ever exist, in any scope.
– ceejayoz
Nov 16 '18 at 2:41
add a comment |
All it means is in this code:
function myFunction() {
carName = "Volvo";
}
carName exists outside myFunction after its execution, and is usable by other code. Whereas:
function myFunction() {
var carName = "Volvo";
}
carName only exists within myFunction, even after it's called. Code outside myFunction can't see it.
answered Nov 16 '18 at 2:35
ceejayozceejayoz
141k34215300
All it means is in this code:
function myFunction() {
carName = "Volvo";
}
carName exists outside myFunction after its execution, and is usable by other code. Whereas:
function myFunction() {
var carName = "Volvo";
}
carName only exists within myFunction, even after it's called. Code outside myFunction can't see it.
answered Nov 16 '18 at 2:35
ceejayozceejayoz
141k34215300
answered Nov 16 '18 at 2:35
ceejayozceejayoz
141k34215300
answered Nov 16 '18 at 2:35
ceejayozceejayoz
141k34215300
answered Nov 16 '18 at 2:35
ceejayozceejayoz
141k34215300
141k34215300
oh i see, it needs to be EXECUTED first...hmm i guess that would make sense
– lilredindy
Nov 16 '18 at 2:39
Right, if you never runmyFunction,carNamedoesn't ever exist, in any scope.
– ceejayoz
Nov 16 '18 at 2:41
add a comment |
oh i see, it needs to be EXECUTED first...hmm i guess that would make sense
– lilredindy
Nov 16 '18 at 2:39
Right, if you never runmyFunction,carNamedoesn't ever exist, in any scope.
– ceejayoz
Nov 16 '18 at 2:41
oh i see, it needs to be EXECUTED first...hmm i guess that would make sense
– lilredindy
Nov 16 '18 at 2:39
oh i see, it needs to be EXECUTED first...hmm i guess that would make sense
– lilredindy
Nov 16 '18 at 2:39
Right, if you never run
myFunction, carName doesn't ever exist, in any scope.– ceejayoz
Nov 16 '18 at 2:41
Right, if you never run
myFunction, carName doesn't ever exist, in any scope.– ceejayoz
Nov 16 '18 at 2:41
add a comment |
expression
var varName = 'value';
declares variable with var varName and then assign a value 'value' to it with = 'value'
expression
varName = 'value';
just making the assignment a value 'value' to a variable 'varName' which should be declared previously
so
function a() {
var varName = 'a'
}
declare the variable varName locally and initiate it with 'a'
but
function b() {
varName = 'b'
}
just assigns the variable varName with the value 'b'. but the variable varName is to be declare in the paren global scope.
answered Nov 16 '18 at 2:46
hypp ersterhypp erster
212
add a comment |
expression
var varName = 'value';
declares variable with var varName and then assign a value 'value' to it with = 'value'
expression
varName = 'value';
just making the assignment a value 'value' to a variable 'varName' which should be declared previously
so
function a() {
var varName = 'a'
}
declare the variable varName locally and initiate it with 'a'
but
function b() {
varName = 'b'
}
just assigns the variable varName with the value 'b'. but the variable varName is to be declare in the paren global scope.
answered Nov 16 '18 at 2:46
hypp ersterhypp erster
212
add a comment |
expression
var varName = 'value';
declares variable with var varName and then assign a value 'value' to it with = 'value'
expression
varName = 'value';
just making the assignment a value 'value' to a variable 'varName' which should be declared previously
so
function a() {
var varName = 'a'
}
declare the variable varName locally and initiate it with 'a'
but
function b() {
varName = 'b'
}
just assigns the variable varName with the value 'b'. but the variable varName is to be declare in the paren global scope.
answered Nov 16 '18 at 2:46
hypp ersterhypp erster
212
expression
var varName = 'value';
declares variable with var varName and then assign a value 'value' to it with = 'value'
expression
varName = 'value';
just making the assignment a value 'value' to a variable 'varName' which should be declared previously
so
function a() {
var varName = 'a'
}
declare the variable varName locally and initiate it with 'a'
but
function b() {
varName = 'b'
}
just assigns the variable varName with the value 'b'. but the variable varName is to be declare in the paren global scope.
answered Nov 16 '18 at 2:46
hypp ersterhypp erster
212
answered Nov 16 '18 at 2:46
hypp ersterhypp erster
212
answered Nov 16 '18 at 2:46
hypp ersterhypp erster
212
answered Nov 16 '18 at 2:46
hypp ersterhypp erster
212
212
add a comment |
add a comment |
When you 'declare' a variable with no explicit declaration keyword (var/let/const), then there is some ambiguity as to whether your intention was to reference an existing variable that may or may not be in a higher scope or to declare a new variable. Much of JavaScript's early defining behavior was to try to have fallback behavior for flexibility. When a variable is assigned to but there is no existing reference, it falls back to creating a variable. And without any declaration keyword there is no way to infer where your intended scope is, so it creates it in a global scope so that other possible references might find it.
In your case, when you call the function it references some variable. JavaScript doesn't know if this was meant to already exist or not, so it creates it in the global scope. As a result, it is still within scope and referenceable after the method is called.
answered Nov 16 '18 at 2:43
msg45fmsg45f
333613
add a comment |
When you 'declare' a variable with no explicit declaration keyword (var/let/const), then there is some ambiguity as to whether your intention was to reference an existing variable that may or may not be in a higher scope or to declare a new variable. Much of JavaScript's early defining behavior was to try to have fallback behavior for flexibility. When a variable is assigned to but there is no existing reference, it falls back to creating a variable. And without any declaration keyword there is no way to infer where your intended scope is, so it creates it in a global scope so that other possible references might find it.
In your case, when you call the function it references some variable. JavaScript doesn't know if this was meant to already exist or not, so it creates it in the global scope. As a result, it is still within scope and referenceable after the method is called.
answered Nov 16 '18 at 2:43
msg45fmsg45f
333613
add a comment |
When you 'declare' a variable with no explicit declaration keyword (var/let/const), then there is some ambiguity as to whether your intention was to reference an existing variable that may or may not be in a higher scope or to declare a new variable. Much of JavaScript's early defining behavior was to try to have fallback behavior for flexibility. When a variable is assigned to but there is no existing reference, it falls back to creating a variable. And without any declaration keyword there is no way to infer where your intended scope is, so it creates it in a global scope so that other possible references might find it.
In your case, when you call the function it references some variable. JavaScript doesn't know if this was meant to already exist or not, so it creates it in the global scope. As a result, it is still within scope and referenceable after the method is called.
answered Nov 16 '18 at 2:43
msg45fmsg45f
333613
When you 'declare' a variable with no explicit declaration keyword (var/let/const), then there is some ambiguity as to whether your intention was to reference an existing variable that may or may not be in a higher scope or to declare a new variable. Much of JavaScript's early defining behavior was to try to have fallback behavior for flexibility. When a variable is assigned to but there is no existing reference, it falls back to creating a variable. And without any declaration keyword there is no way to infer where your intended scope is, so it creates it in a global scope so that other possible references might find it.
In your case, when you call the function it references some variable. JavaScript doesn't know if this was meant to already exist or not, so it creates it in the global scope. As a result, it is still within scope and referenceable after the method is called.
answered Nov 16 '18 at 2:43
msg45fmsg45f
333613
answered Nov 16 '18 at 2:43
msg45fmsg45f
333613
answered Nov 16 '18 at 2:43
msg45fmsg45f
333613
answered Nov 16 '18 at 2:43
msg45fmsg45f
333613
333613
add a comment |
add a comment |
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Possible duplicate of What is the scope of variables in JavaScript?
– Abana Clara
Nov 16 '18 at 2:39