The main problem with checking if a variable exists is that it can be slow.
if (typeof variable !== 'undefined') {
// the variable is defined
}
The first line is an if statement. It checks if the type of the variable is not equal to ‘undefined’. If it is not, then it runs the code inside the curly braces. This code just prints a message saying that the variable is defined.
If exist method
The IfExists method is a built-in function in JavaScript that checks to see if a specified condition is true. If it is, the function returns a value; otherwise, it returns null.
variables and loops
In JavaScript, variables are declared using the var keyword and can be assigned values using the = operator. Loops are created using the for statement and can be used to repeat a set of code a certain number of times.
