created hoisting.md

docs/JavaScript_Advance/hoisting.md

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+# what is hoisting?
+
+Basically, when Javascript compiles all of your code, all variable declarations using var are hoisted/lifted to the top of their functional/local scope (if declared inside a function) or to the top of their global scope (if declared outside of a function) regardless of where the actual declaration has been made. This is what we mean by “hoisting”.
+
+
+In JavaScript, a variable can be declared after it has been used. In other words; a variable can be used before it has been declared.
+
+Example 1 gives the same result as Example 2:
+```
+Example 1 :
+
+x = 5; // Assign 5 to x
+
+elem = document.getElementById("demo"); // Find an element
+elem.innerHTML = x; // Display x in the element
+
+var x; // Declare x
+```
+```
+Example 2:
+var x; // Declare x
+x = 5; // Assign 5 to x
+
+elem = document.getElementById("demo"); // Find an element
+elem.innerHTML = x; 
+```
+
+To understand this, you have to understand the term "hoisting".
+
+Hoisting is JavaScript's default behavior of moving all declarations to the top of the current scope (to the top of the current script or the current function).