Hoisting is an action of javascript interpreter which moves all declarations to the top.
Why hoisting matters? Consider the example shown below.
foo();
var foo = function() {
alert('Hi');
}This example generates an exeption due to calling non-function variable. Because the code shown above actually translates to the following code.
var foo;
foo();
foo = function() {
alert('Hi');
}How about the following example?
foo();
function foo() {
alert('Hi');
}This example will work due to function declaration hoisting.
Quiz
What is the result of executing this code?
function test() {
console.log(a);
console.log(foo());
var a = 1;
function foo() {
return 2;
}
}
test();