Using function.prototype.bind directly on function declaration

Question

Why is this allowed ?

var f = function() {
  console.log(this.x);
}.bind({x:1})();

And why this is not or better why I get syntax error in this case ?

function f() {
  console.log(this.x);
}.bind({x:1})();

So, why I need function expression syntax to get this work and is there a way to use bind method directly on function declaration ?

A function declaration is not an expression, so you can't do that. But you can force an expression !function f(){}.bind({x:1})(). Look for info on IIFE. — elclanrs
– elclanrs, Commented Apr 9, 2015 at 0:20
Because it is not an expression. The syntax is ambiguous, you have to disambiguate by forcing an expression. Check the spec for more info ecma-international.org/ecma-262/5.1/#sec-13 — elclanrs
– elclanrs, Commented Apr 9, 2015 at 0:34
Thanks, this is one more reason for throwing away function declaration and always using expression form. I can use methods directly, no hoisting... — user3448600
– user3448600, Commented Apr 9, 2015 at 0:39

Halcyon · Accepted Answer · 2015-04-09 00:21:16Z

5

The second example works but the syntax is slightly off:

Surround the function in parens. I have to say that I'm not entirely sure why. It seems like it would work without the parens huh? :P

(function f() {
    console.log(this.x);
}).bind({x:1})();

answered Apr 9, 2015 at 0:21

Halcyon

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1 Comment

parens make an expression, and thus an anon function, and thus a "tail value". you can also do the prefix-only alternative to paren wraps: 0||