Variables are the building blocks of any programming language. In JavaScript, you often need to check if the variable exists, in other words, it has been declared and initialized in the code.
How to Check If the Variable is Declared and Initialized
To check if a variable exists in JavaScript, you can use the typeof operator. The typeof operator returns a string that represents the type of the operand. If the operand is a variable that has not been declared or initialized, typeof will return "undefined". Here is an example of how to use typeof operand in JavaScript.
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let myVariable; if (typeof myVariable !== "undefined") { console.log("myVariable is defined"); } else { console.log("myVariable is not defined"); } |
In the example above, the if statement will evaluate to false because myVariable has not been initialized with a value. The else block will be executed and the string "myVariable is not defined" will be printed to the console.
Please Note that this method will not work if the variable has been declared but not initialized with a value.
Conclusion
You can use the typeof operator to check if the variable exists in the code. The typeof operand will return undefined if the variable is not initialized with a value otherwise it will return the type of the value stored in it. You can read more about the typeof operator in JavaScript.