CODEWITHSUNDEEP
javascript
Valentin H
Valentin H

Reputation: 7448

String literals concatination. What does this syntax mean in JS?

I've just found a decent bug in my JS code, which I'm porting from C++:

var x = "aaa"
        "bbb";

//In C++: x="aaabbb" 
//In JS: x="aaa"

Surprisingly there were no error (in node.js).

How does JS handle "bbb"?

Upvotes: 2

Views: 60

Answers (3)

AmmarCSE
AmmarCSE

Reputation: 30597

Semi-colons are not required in javascript to end a statement. Those statements were interpreted as set x to "aaa" and execute next statement "bbb" which is just an arbitrary string.

You can think of it as the semi-colon being auto inserted so the statements become

var x = "aaa";"bbb";

Upvotes: 3

elclanrs
elclanrs

Reputation: 94121

It doesn't handle it. What happens is that JavaScript will insert a semicolon for you, and "bbb" is merely an expression:

var x = "aaa"; // JS inserts this semicolon
"bbb"; // this is a valid expression but does nothing

This feature is known as ASI. If you put a + it will concatenate the strings:

var x = "aaa" +
        "bbb";

Upvotes: 2

Luke
Luke

Reputation: 5708

JavaScript is inserting a semicolon after the first line.

So, what you're really doing is 

var  x = "aaa";
         "bbb";

It evaluates the first line, which assigns "aaa" to x and then evaluates the second line which doesn't assign "bbb" to anything.

You might want to see this question about the rules for semicolon insertion in JS

Upvotes: 2

Related Questions