在javascript中声明和定义函数

Question

I have a doubt regarding functions(objects) in javascript.

I have 2 pieces of code like,

    var a= function(){
    console.log('abc')
     }

and

     var a= (function(){
     console.log('abc')
     })

what is the difference between these two>>
thanx:)

Answer 1

There is no difference now, but if you add another parenthesis () after second function it will run function without invocation.

 var a= (function(){
     console.log('abc')
     })()

it will print 'abc' straightaway

Answer 2

There is no difference. You have a function expression, and you can put any number of parentheses around an expression.

Just as this:

a = 42;

is the same as this:

a = (42);

and this:

a = (((((42)))));

Answer 3

There is no practical difference. They will both result in an anonymous function being assigned to a .

The first is a " simple assignment ". In the second, the parentheses are acting as a " grouping operator ", which does one thing:

The production PrimaryExpression : ( Expression ) is evaluated as follows:

• Return the result of evaluating Expression. This may be of type Reference.

So the grouping operator will return the function contained within it, and assign it to a , just like the first example.

Answer 4

There is a difference.

( and ) constitute a grouping. A grouping can only contain an expression, thus any function inside it will be an expression and not a declaration.

Since ECMA specifies that a function declaration must always have a function name, and a function expression may omit it, you will be able to do the following

(function() {});

while the following declaration is not valid

function() {};

It won't matter that often, but still... Read this in-depth article for more: http://kangax.github.com/nfe/

Answer 5

As has been said, the two examples you've given are essentially the same.

This question has a lot more information contained in the answers regarding parentheses usage, might be worth your time to spin through!

Why are parenthesis used to wrap a javascript function call?