What's the reason for the alert not functioning properly?

Question

What's the reason for the alert not functioning properly?

I am curious about the distinction between declaring a variable using var. To explore this, I tried the following code:

<body>
    <h1>New Web Project Page</h1>
    <script type="text/javascript">
        function test(){
            a = "hello";
            var b="world";
        }
        alert(a);
        alert(b);


    </script>
</body>

I am puzzled as to why the alerts are not working and what exactly is the difference when variables are declared with or without the use of var in JavaScript.

javascript

Answer 1

Answer №1

alert isn't effective in this scenario because b doesn't exist in the correct scope, and a hasn't been instantiated as you haven't invoked the function test.

var is used to create a variable that is local to its calling scope. Without using var, a global variable is created instead.

function fn ( ) {
    var x = 0; // this variable is only visible within the function fn

    y = 10; // this variable is global and accessible from anywhere after calling fn
}

In general, it's advisable to avoid using global variables unless necessary. It's recommended to declare all variables with var to keep code easy to understand and maintain. This practice also helps prevent the issue of "Magic Variables," where variables seem to appear out of nowhere. By following this approach, debugging becomes easier as well since JavaScript automatically creates non-existent variables. However, by utilizing only local variables through var and tools like jsLint, you can prevent issues like misspelling variable names disrupting your code.

Answer 2

alert isn't effective in this scenario because b doesn't exist in the correct scope, and a hasn't been instantiated as you haven't invoked the function test.

var is used to create a variable that is local to its calling scope. Without using var, a global variable is created instead.

function fn ( ) {
    var x = 0; // this variable is only visible within the function fn

    y = 10; // this variable is global and accessible from anywhere after calling fn
}

In general, it's advisable to avoid using global variables unless necessary. It's recommended to declare all variables with var to keep code easy to understand and maintain. This practice also helps prevent the issue of "Magic Variables," where variables seem to appear out of nowhere. By following this approach, debugging becomes easier as well since JavaScript automatically creates non-existent variables. However, by utilizing only local variables through var and tools like jsLint, you can prevent issues like misspelling variable names disrupting your code.

Answer 3

Answer №2

When a variable is declared without using var, it becomes global and can be accessed by anything within the scope. The reason why your alert isn't working is because you have not called the function test(), which means that variables a and b are never assigned any values. If you do call test() before the alerts, b will be undefined while a should return "hello".

For more information on variables and scoping, check out this helpful resource.

Answer 4

When a variable is declared without using var, it becomes global and can be accessed by anything within the scope. The reason why your alert isn't working is because you have not called the function test(), which means that variables a and b are never assigned any values. If you do call test() before the alerts, b will be undefined while a should return "hello".

For more information on variables and scoping, check out this helpful resource.

Answer 5

Answer №3

Be sure to call the test() function. If you omit the var, the variables are declared globally and can be accessed by any part of the code.

Answer 6

Be sure to call the test() function. If you omit the var, the variables are declared globally and can be accessed by any part of the code.

Answer 7

Answer №4

A similar question about the usage of 'var' has already been addressed here

As for why your alert isn't working, it's because you haven't invoked the 'test()' function. Simply defining it won't trigger any action. Make sure to call the function to populate the variables.

Answer 8

A similar question about the usage of 'var' has already been addressed here

As for why your alert isn't working, it's because you haven't invoked the 'test()' function. Simply defining it won't trigger any action. Make sure to call the function to populate the variables.

What's the reason for the alert not functioning properly?

Answer №1

Answer №2

Answer №3

Answer №4

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