<script>
function makeArray(arg1, arg2){
return [ this, arg1, arg2 ];
}
alert(window.makeArray('one', 'two'));
</script>
Question:
The output of the above script is: [Object Window], one, two, If I changed return [ this, arg1, arg2 ]; to return ( this, arg1, arg2 ); the output is: two. So what is the difference between return[] and return()?
return does not support returning multiple arguments. Nor does it require braces for its argument, so when you call:
return (this, 'one', 'two');
then the braces simply enclose a single expression, where the result of that expression is what's returned to the caller.
Inside that expression you've actually used the "comma operator" (twice).
The comma expression a, b evaluates both a and b, but the result of the expression is just b (i.e. the right hand operand).
In your case you've written (a, b, c), equivalent to ((a, b), c), hence still returning the rightmost operand (i.e. "two")
This other question might be useful.
Essentially, if you have return[], really return [], your return value is a list of items. In comparison, return(x) is just another way to call return x.
As mentioned by @Alnitak, in return(a, 'one', 'two') you are returning an expression using the comma operator.
This returns an array with three elements. In Javascript, the [] is for array notation.
return [ this, arg1, arg2 ];
Whereas this causes the expression to be evaluated, and the last argument will always be returned (arg2):
return ( this, arg1, arg2 );
To deomonstrate:
console.log( ('a', 'b', 'c') ); // c
console.log( ('a', 'b', false) ); // false
console.log( (true, false, 0) ); // 0
There is no special construct like return[] or return(). It's always just return <some expression>.
Square brackets is an array literal, thus you get an array as returned value. () is just parenthesis and x, y is always y (lookup comma operator).
forhead in general:for(i=0, a=[]; i<10; i++)returnis well documented, but no one ever wrote up the bad things that happen if you inadvertently try to combine them.return (a, b)kinda looks like exactly a function call with a list of arguments. Except that it isn't.