The behavior of the += operator is dependent on the data type of the initial variable. The += operator can either perform string concatenation or numeric addition, depending on the initial value.

Here’s how it works:

1. If the Initial Variable is a String:

• The += operator will perform string concatenation.
• Anything added to a string will be converted into a string and appended.

Example (String Concatenation):

let hexColor = "#"; // String
hexColor += 5; // "5" is concatenated to hexColor, not added as a number
hexColor += 3; // "3" is also concatenated

console.log(hexColor); // Output: "#53"

2. If the Initial Variable is a Number:

• The += operator will perform numeric addition.
• Only numbers will be added, and no type conversion happens.

Example (Numeric Addition):

let totalSum = 0; // Number
totalSum += 5; // Adds 5 to totalSum
totalSum += 3; // Adds 3 to totalSum

console.log(totalSum); // Output: 8

Key Takeaways:

• If the initial variable is a string, += will concatenate values as strings. This applies even if you try to add numbers — they will be treated as strings and appended to the end.
• If the initial variable is a number, += will perform addition, and the values on the right-hand side must be numbers.