"Hoisting" in JavaScript refers to the behavior in which variable and function declarations are moved to their top scopes during the compilation phase, before the actual code execution. This means that you can use a variable or function before you have declared it in code.
In the variables declared with "var" case, the declaration is moved to the top and initialized with "undefined". In the case of functions and variables declared with "let" and "const", the declaration is moved to the top, but initialization does not occur until the point where the code reaches the declaration line.
Here are some examples to illustrate hoisting.
Example with var
console.log(a); // undefined
var a = 5;
console.log(a); // 5
var a = 5;
console.log(a); // 5
In the example above, the declaration and initialization of variable "a" are moved to the top. Therefore, the first "console.log(a)" statement does not generate an error, but prints "undefined", because initialization occurs only on the second line.
Example with let
console.log(b); // ReferenceError: b is not defined
let b = 10;
console.log(b); // 10
let b = 10;
console.log(b); // 10
In this case, the declaration of "b" is moved to the top, but initialization does not occur until the line where "let b = 10;" is present. The first "console.log(b)" statement results in an error because "b" has not yet been defined at this point.
Example with function
hoistedFunction(); // works even before the declarationfunction hoistedFunction() {
console.log("Hello, hoisting!");
}
Functions declared using the "function" keyword are also hoisted, so you can call the function before its declaration in the code.
It's important to understand hoisting when working with JavaScript to avoid unexpected behavior and bugs. It is recommended to declare your variables and functions at the beginning of the scope to make the code more readable and avoid surprises related to hoisting.
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