I am using JavaScript and I create a global variable. I define it outside of a function and I want to change the global variable value from inside a function and use it from another function, how do I do this?
Necreaux
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asked Jun 3, 2012 at 16:30
NullPoiиteяNullPoiиteя
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Just reference the variable inside the function; no magic, just use it's name. If it's been created globally, then you'll be updating the global variable.
You can override this behaviour by declaring it locally using var, but if you don't use var, then a variable name used in a function will be global if that variable has been declared globally.
That's why it's considered best practice to always declare your variables explicitly with var. Because if you forget it, you can start messing with globals by
accident. It's an easy mistake to make. But in your case, this turn around and becomes an easy answer to your question.
answered Jun 3, 2012 at 22:41
6
var a = 10;
myFunction[];
function myFunction[]{
a = 20;
}
alert["Value of 'a' outside the function " + a]; //outputs 20
NullPoiиteя
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answered Jun 3, 2012 at 16:34
ChrisChris
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Just use the name of that variable.
In JavaScript,
variables are only local to a function, if they are the function's parameter[s] or if you declare them as local explicitely by typing the var keyword before the name of the variable.
If the name of the local value has the same name as the global value, use the window object
See this jsfiddle
x = 1;
y = 2;
z = 3;
function a[y] {
// y is local to the function, because it is a function parameter
console.log['local y: should be 10:', y]; // local y through function parameter
y = 3; // will only overwrite local y, not 'global' y
console.log['local y: should be 3:', y]; // local y
// global value could be accessed by referencing through window object
console.log['global y: should be 2:', window.y] // global y, different from local y []
var x; // makes x a local variable
x = 4; // only overwrites local x
console.log['local x: should be 4:', x]; // local x
z = 5; // overwrites global z, because there is no local z
console.log['local z: should be 5:', z]; // local z, same as global
console.log['global z: should be 5 5:', window.z, z] // global z, same as z, because z is not local
}
a[10];
console.log['global x: should be 1:', x]; // global x
console.log['global y: should be 2:', y]; // global y
console.log['global z: should be 5:', z]; // global z, overwritten in function aEdit
With
ES2015 there came two more keywords const and let, which also affect the scope of a variable [Language Specification]
answered Jun 3, 2012 at 16:35
yunzenyunzen
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var a = 10;
myFunction[a];
function myFunction[a]{
window['a'] = 20; // or window.a
}
alert["Value of 'a' outside the function " + a]; //outputs 20
With window['variableName'] or window.variableName you can modify the value of a global variable inside a function.
answered Mar 28, 2018 at 3:54
Sterling DiazSterling Diaz
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var x = 2; //X is global and value is 2.
function myFunction[]
{
x = 7; //x is local variable and value is 7.
}
myFunction[];
alert[x]; //x is gobal variable and the value is 7
answered Mar 10, 2014 at 8:22
Iman SedighiIman Sedighi
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A simple way is to use var
var apple = null;
const some_func =[]=>{
apple = 25
}
some_func[]
console.log[apple]
answered Mar 27, 2021 at 23:52
1