What is the default scope of a variable declared with 'var' in JavaScript?
Answers
Local scope
Block scope
Global scope
Function scope
# Understanding the Default Scope of Variables in JavaScript
When a variable is declared with `var` in JavaScript, it is given a 'Global scope' by default. This means that it becomes accessible anywhere within your code - not just within the block of code where it has been defined.
Take for example the following JavaScript code,
```javascript
var myVariable = "Hello, world!";
function myFunction() {
console.log(myVariable);
}
myFunction(); // This will log 'Hello, world!'
```
In this example, `myVariable` is defined outside the `myFunction()`. But since `var` gives the variable a 'Global scope', it can be freely accessed and used inside `myFunction()`. Therefore, when `myFunction()` is called, it successfully logs the value stored in `myVariable`.
It's also important to note that because variables declared with `var` have 'Global scope', they can accidentally overwrite other variables with the same names, potentially leading to bugs within your code.
Consider the following code snippet:
```javascript
var myVariable = "This is global!";
function myFunction() {
var myVariable = "This is local!";
console.log(myVariable);
}
myFunction(); // This will log 'This is local!'
console.log(myVariable); // This will log 'This is global!'
```
In this instance, `myVariable` is defined twice. Once on a global level and once inside `myFunction()`. They are treated as two separate variables. The 'Global scope' variable isn't overwritten by the 'Local scope' variable because they exist in different scopes.
Though JavaScript allows variables to have a 'Global scope', it is generally a good practice to keep the usage of 'Global scope' variables to a minimum and use 'Local scope' variables (like `const` and `let`) as much as possible to prevent potential naming conflicts and bugs.
Best practices and code readability should always be a top priority when writing code in any language, including JavaScript.