String concatenation
Learn to concatenate strings with + and the common mistakes around it.
Joining strings with +
You use the + operator to glue two strings together. This is called concatenation.
For example "Alex" + " " + "Smith" gives "Alex Smith". Without a space the strings stick directly: "Alex" + "Smith" becomes "AlexSmith".
You can chain many pieces with + in a row. The operation runs left to right; parentheses change the order.
Adding a string and a number
The + operator joins two strings; but if one side is a number JavaScript checks a rule. When either side is a string, + performs concatenation and the number is turned into a string.
For example "Result: " + 5 gives "Result: 5". The number is first converted to a string and then joined.
When both sides are numbers normal addition happens: 3 + 5 → 8. Use typeof to see which type you are dealing with.
Exercise Concatenate the full name
Declare firstName as "Alex" and lastName as "Smith". Build fullName as firstName + " " + lastName. Log fullName with console.log.
Show example solution
const firstName = "Alex";
const lastName = "Smith";
const fullName = firstName + " " + lastName;
console.log(fullName);Test yourself
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What does "Alex" + " " + "Smith" give?
console.log("Ayşe" + " " + "Yılmaz");- "Alex Smith"
- "AlexSmith"
- "Alex+Smith"
- "Alex" "Smith"
Show answer
"Alex Smith" — Correct. + pastes each piece in order; the middle " " space ends up in the result.
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Concatenate the score
const score = 90; const message = "Skor: " + ____;Show answer
const score = 90; const message = "Skor: " + score; -
Match each expression to its result
- "a" + "b"
- "ab"
- "x" + 5
- "x5"
- 3 + 5
- 8
- "3" + "5"
- "35"
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What does "Value: " + 5 give?
console.log("Değer: " + 5);- 10
- "Value: " + 5
- "Value: 5"
- "Value: "
Show answer
"Value: 5" — Correct. With a string on one side, + concatenates; 5 is turned into a string and appended.