Your calculator likely displays "undefined" when deleting the last character because of how your code is handling the input string or expression. When the input becomes empty (e.g., after deleting all characters), the expression is no longer valid, and the result of evaluating it is undefined. Here are a few potential causes and solutions:
---
1. Directly Evaluating an Empty String
If you are using eval() or a similar function to evaluate the expression, passing an empty string results in an error or an "undefined" output.
Solution: Before evaluating the input, check if it's empty:
2. No Default Value for an Empty Input
If you don't handle what should be displayed when the input is empty, your program may display "undefined" as there's no valid expression to evaluate.
Solution: Set a default value (e.g., 0) when the input is cleared:
3. Removing the Last Character Without Revalidating
If you remove the last character from the input string without checking if it makes the expression invalid, the program might attempt to evaluate an incomplete or empty expression.
Solution: Ensure you revalidate the input after every modification:
4. Attempting to Display a Result When Input Is Invalid
If your code always tries to compute and display a result, even when the input is invalid (e.g., empty), "undefined" may appear.
Solution: Add error handling or only compute when the input is valid:
Debugging Tip:
Use console.log(input) to inspect what the input becomes after each deletion.
Ensure your code gracefully handles empty inputs and incomplete ex
pressions.
---
1. Directly Evaluating an Empty String
If you are using eval() or a similar function to evaluate the expression, passing an empty string results in an error or an "undefined" output.
Solution: Before evaluating the input, check if it's empty:
JavaScript:
if (input === "") {
display.innerText = "0"; // Or any default value
} else {
display.innerText = eval(input);
}
---2. No Default Value for an Empty Input
If you don't handle what should be displayed when the input is empty, your program may display "undefined" as there's no valid expression to evaluate.
Solution: Set a default value (e.g., 0) when the input is cleared:
JavaScript:
if (input.length === 0) {
display.innerText = "0";
}
---3. Removing the Last Character Without Revalidating
If you remove the last character from the input string without checking if it makes the expression invalid, the program might attempt to evaluate an incomplete or empty expression.
Solution: Ensure you revalidate the input after every modification:
JavaScript:
input = input.slice(0, -1); // Remove the last character
if (input.length === 0) {
display.innerText = "0";
} else {
display.innerText = eval(input);
}
---4. Attempting to Display a Result When Input Is Invalid
If your code always tries to compute and display a result, even when the input is invalid (e.g., empty), "undefined" may appear.
Solution: Add error handling or only compute when the input is valid:
JavaScript:
try {
display.innerText = input ? eval(input) : "0";
} catch (error) {
display.innerText = "Error";
}
---Debugging Tip:
Use console.log(input) to inspect what the input becomes after each deletion.
Ensure your code gracefully handles empty inputs and incomplete ex
pressions.