Understanding Local and Global Variables in JavaScript
Like other programming languages, JavaScript also has local and global variables. But the declaration and scope of a variable in JavaScript is different from others programming languages. In this article, I am going to explain the difference between local and global variables in JavaScript.
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Types of Variables in JavaScript
JavaScript Local Variable
A variable that is declared inside a function definition is called local and has scope to that function only. JavaScript does not support block scope in which a set of curly braces {. . .} defines a new scope.
<script> // Global variable. var a = "Dot Net Tricks !"; function Show() { // A local variable is declared in this function. var a = "Hello World !"; alert("Value of 'a' inside the function " + a); //Hello World ! } alert("Value of 'a' outside the function : " + a); //Dot Net Tricks ! </script>
JavaScript Global Variable
A variable that is declared outside of a function definition is called a global variable and its scope is throughout your program means its value is accessible and modifiable throughout your program.
<script > // Global variable. var a = "Dot Net Tricks !"; function Show() { // A Local variable is declared in this function. var a = "Hello World !"; alert("Value of 'a' inside the function :" + a); //Hello World ! //b will have global scope b = "Hello JavaScript !"; Display(); } alert("Value of 'a' outside the function : " + a); //Dot Net Tricks ! function Display() { //Since b variable has global scope alert("Value of 'b' outside the function : " + b); //Hello JavaScript ! } </script>
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Note
A variable that is declared inside a function using the var keyword, will have a local scope.
A variable that is declared inside a function without var keyword, will have a global scope means acts like a global variable.
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