Difference Between Eval And Settimeout Execute String Code

I know that eval and setTimeout can both accept a string as the (1 st) parameter, and I know that I'd better not use this. I'm just curious why is there a difference: !function() {

Solution 1:

See the reference of setTimeout on MDN.

String literals are evaluated in the global context, so local symbols in the context where setTimeout() was called will not be available when the string is evaluated as code.

In contrast, the string literal passed to eval() is executed in the context of the call to eval.

Solution 2:

setTimeout's eval is additionally executed in global scope, so it's not aware of foo.

Here's reference to back it up:

String literals are evaluated in the global context, so local symbols in the context where setTimeout() was called will not be available when the string is evaluated as code.

Solution 3:

setTimeout takes more parameters than function reference and timeout. Anything entered past timeout will be passed to your function as a parameter.

setTimeout(myFunction(param1, param2), 0, param1, param2);

Solution 4:

As a complement to the correct answer, here is a call to eval that would give you the same behavior, and error in this cases:

!function() {
    var foo = 123;
    window.eval("alert(foo)"); // <- note the window.eval, this is important and changes the behavior of the `eval` function
}();

!function() {
    var foo = 123;
    setTimeout("alert(foo)", 0);
}();

This blog post goes in depth on the different types of eval: http://perfectionkills.com/global-eval-what-are-the-options/