I understand Hoisting of variables is done in Java Script. I am unable to get why it outputs as undefined
do_something()
{
var foo = 2;
console.log(foo);
} do_something() // it prints 2
do_something()
{
console.log(foo); var foo = 2;
} do_something() // it prints undefined
As javascript do hoisting the second function also should print 2 as per my understand.buy why doesn't it
This is how the interpreter sees your code,
do_something() {
var foo;
console.log(foo); // undefined
foo = 2;
}
do_something();
So it is printing undefined. This is a basic of variable hoisting. Your declarations will be moved to the top, and your assignation will remain in the same place. And the case is different when you use let over var.
Javascript only hoists declarations, not initializations.
var x = y, y = 'A';
console.log(x + y); // undefinedA
Here, x and y are declared before any code is executed, the assignments occur later. At the time "x = y" is evaluated, y exists so no ReferenceError is thrown and its value is 'undefined'. So, x is assigned the undefined value. Then, y is assigned a value of 'A'. Consequently, after the first line, x === undefined && y === 'A', hence the result.
Only the declaration is hoisted. the assigned variables are not hoisted. So you are
The second function outputs undefined because you set the variable after you called it. The code you wrote is synchronous which means its read by the interpreter line by line, executed in order. If you don't define the variable before calling it, the console outputs undefined.
Only the declaration is hoisted, any assignment to a variable always stays where its originally from.
