JS Isset - Javascript

In PHP, there is a function called isset() which checks if a variable exists and is not null. However, in JavaScript, there is no direct equivalent to isset(). This can be a problem for developers who need to check if a variable is defined before using it.

In this article, we will explore some ways of checking if a variable is defined in JavaScript.

Using typeof

One way of checking if a variable is defined is by using the typeof operator. The typeof operator returns the type of the operand.

if (typeof variable !== 'undefined') {
    // variable is defined
} else {
    // variable is not defined
}

In this case, we are using the typeof operator to check if the variable variable is defined. If the variable is defined, it will return the type of the variable, which is not 'undefined'.

Using the in operator

Another way of checking if a variable is defined is by using the in operator.

if ('variable' in window) {
    // variable is defined
} else {
    // variable is not defined
}

In this case, we are using the in operator to check if the variable variable is defined in the window object. If the variable is defined, it will return true.

Using a try-catch block

You can also check if a variable is defined using a try-catch block.

try {
    variable;
    // variable is defined
} catch (e) {
    // variable is not defined
}

In this case, we are trying to access the variable variable inside a try block. If the variable is defined, the code inside the try block will execute without any errors. If the variable is not defined, the code inside the catch block will execute.

Conclusion

In summary, there is no direct equivalent to isset() in JavaScript, but there are several ways of checking if a variable is defined. You can use the typeof operator, the in operator, or a try-catch block to check if a variable is defined.