Reputation: 3011

Javascript defining object, comma case

While I was trying some fundemantels in Javascript, I came across a question, which suprised me, and I cannot find an answer to that. I got the following, which works perfecty:

var obj= new Object ();
    obj.test = "Hello" 

    obj.testTwo= function (){
        console.log(this.test)
    },obj.testTwo();

When I'm trying it without a comma, it does not work.

var obj= new Object ();
    obj.test = "Hello" 

    obj.testTwo= function (){
        console.log(this.test)
    }obj.testTwo();

So I tried this as a third option...and it works?

var obj= new Object ();
    obj.test = "Hello" 

    obj.testTwo= function (){
        console.log(this.test)
    }
    obj.testTwo();

Now I'm quiet confused. Why to use a comma and why does it work with a break?

Upvotes: 0

Answers (4)

Teemu

Reputation: 23396

In the first snippet, the comma operator does its duty as it is documentated: "evaluates both of its operands (from left to right) and returns the value of the second operand." ^MDN.

Basicly your second snippet is an assignment. Assignments should always be terminated with a semicolon, even if their last expression would be a block of statements. However, this is not obvious to ASI. Hence this snippet fails without either a semicolon or a newline between the block and object method call, where interpreter expects to see an operator or a termination of the assignment. If none of these is found, an Unexpected token error is thrown. This same explanation stands for why the third snippet works.

Upvotes: 2