In JavaScript, you can use ternary operators to check if a variable exists or is defined. Ternary operators provide a concise way of writing conditional statements in a single line of code.

Here’s an example of how you can use ternary operators to check the existence of a variable:

const myVariable = "Hello, world!";

const variableExists = typeof myVariable !== "undefined" ? true : false;

console.log(variableExists); // Output: true

In the above code, we first declare the variable myVariable and assign it a value of “Hello, world!”. Then, we use the ternary operator to check if myVariable is defined by comparing its type with the string “undefined”. If the condition evaluates to true, the variableExists variable is assigned the value true. Otherwise, it is assigned the value false.

Finally, we log the value of variableExists to the console, which outputs true since myVariable is defined.

Using a ternary operator like this is a concise and efficient way to check if a variable exists in JavaScript. It avoids the need for longer if-else statements and reduces the code complexity.

Remember to always leverage JavaScript’s built-in operators and language features to write clean and efficient code.