I have a doubt, I have always coded in js but I always did not use the var to put in the declaration of a variable but I saw that some say that var should be put inside a function, others say that it is put when it is out.
Thanks for your contributions.
Depends on the javascript version.
If you use JS5 (the standard in browsers) var is the keyword used to declare a variable. Ex:
var miVariable, otraVariableInicializada=1,
otraVariableUndefined;
Now if you use Javascript 6 (ECMAScript 2015) or higher (NodeJS), the keyword var has fewer uses.
In general, use the const (for constants and functions) or let (for variables) unless you need to create a closure , in which case var should be used.
const modulo = require('modulo');
const miFunc = () => {
var enClousure = 1234;
return () => {
let valorLocal = modulo.getAlgo();
return enClousure + valorLocal;
};
};
Here is an example that my professor gave me in his day to see if you understand.
function f1(a,b){
var c=c+a; // La variable c es LOCAL
d=d+b; // La variable d es GLOBAL
document.write("En f1()<br/>");
document.write("c="+c+"<br/>");
document.write("d="+d+"<br/>");
}
function f2(){
document.write("En f2()<br/>");
document.write("c="+c+"<br/>");
document.write("d="+d+"<br/>");
}
// ---------------------------------------
var c = 10; // Variable GLOBAL. Es un script
d = 20; // Variable GLOBAL
f1(1,2);
f2(); When you declare a variable without putting the var in front, you are declaring that variable globally to the entire document *.js instead if you put var variable you are declaring local to the method that you are going to use.
If you put var you can use it inside but not outside where it was declared; Example as a variable name behaves depending on where it was declared; even the declared without "var" inside the function remains global to the page.