JavaScript syntax
part 7/43 · 161.3 KB total
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Examples
Here are some examples of variable declarations and scope:
var x1 = 0; // A global variable, because it is not in any function
let x2 = 0; // Also global, this time because it is not in any block
function f() {
var z = 'foxes', r = 'birds'; // 2 local variables
m = 'fish'; // global, because it was not declared anywhere before
function child() {
var r = 'monkeys'; // This variable is local and does not affect the
"birds" r of the parent function.
z = 'penguins'; // Closure: Child function is able to access the
variables of the parent function.
}
twenty = 20; // This variable is declared on the next line, but usable
anywhere in the function, even before, as here
var twenty;
child();
return x1 + x2; // We can use x1 and x2 here, because they are global
}
f();
console.log(z); // This line will raise a ReferenceError exception,
because the value of z is no longer available
for (let i = 0; i < 10; i++) console.log(i);
console.log(i); // throws a ReferenceError: i is not defined
for (const i = 0; i < 10; i++) console.log(i); // throws a TypeError:
Assignment to constant variable
for (const i of [1,2,3]) console.log(i); //will not raise an exception.
i is not reassigned but recreated in every iteration
const pi; // throws a SyntaxError: Missing initializer in const
declaration
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