for (var i=10; i; i--) { 
    (function() { return i; })(); 
} 

while(i) { 
    var a = function() { return i; }; 
    a(); 
} 

do { 
    function a() { return i; }; 
    a(); 
} while (i); 

let foo = 0; 
for (let i=10; i; i--) { 
    // Bad, function is referencing block scoped variable in the outer scope. 
    var a = function() { return foo; }; 
    a(); 
}

var a = function() {}; 

for (var i=10; i; i--) { 
    a(); 
} 

for (var i=10; i; i--) { 
    var a = function() {}; // OK, no references to variables in the outer scopes. 
    a(); 
} 

for (let i=10; i; i--) { 
    var a = function() { return i; }; // OK, all references are referring to block scoped variables in the loop. 
    a(); 
} 

var foo = 100; 
for (let i=10; i; i--) { 
    var a = function() { return foo; }; // OK, all references are referring to never modified variables. 
    a(); 
}