Why Does My JavaScript Code Concatenate Instead of Adding Numbers?

Overcoming JavaScript's String Concatenation Math Trap

In JavaScript, manipulating variables can sometimes lead to unintended outcomes. A common pitfall is the concatenation of strings instead of performing mathematical operations. This can occur when a numeric variable is treated as a string, leading to the addition of strings rather than numbers.

Scenario: Integer Addition with Unexpected String Result

For example, consider the following code:

var dots = document.getElementById("txt").value; // 5
function increase() {
    dots = dots + 5;
}

We expect this code to increase the value of dots by 5. However, the output is "55" instead of 10. This is because the variable dots is treated as a string, and JavaScript concatenates strings instead of performing mathematical operations.

Solution: Force Mathematical Operation

To resolve this issue, we need to force JavaScript to treat dots as an integer and perform mathematical operations. We can do this by using the parseInt() function:

dots = parseInt(document.getElementById("txt").value, 10);

• The parseInt() function converts the string dots to an integer.
• The second parameter, 10, specifies the base-10 number system.

By converting dots to an integer, JavaScript will correctly perform mathematical operations on it, resulting in the desired output of 10.

Remember, when handling numeric variables in JavaScript, be cautious of potential type conversion issues that could result in string concatenation instead of mathematical operations. By using techniques like parseInt(), you can ensure that JavaScript performs the intended calculations.

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