What does this option do?

The JSHint latedef option is used to ensure variables and functions are declared before they are used. That is to say, the declarations appear physically in the source code above references to those declared variables or functions. Because declarations in JavaScript are hoisted to the top of the scope in which they occur it is perfectly safe to reference them earlier.

In the following example the doStuff function declaration is hoisted to the top of the global scope so it is accessible throughout the program regardless of its position in the source:

/*jshint latedef: true */
doStuff();
function doStuff() {}

When should I use this option?

The use of the latedef JSHint option will cause a "'{a}' was used before it was defined" error any time it encounters a reference to an identifier that has not yet been declared. By declaring variables and functions before you need to refer to them you can make your code easier to read through, since most people will read it from top to bottom. If a function is declared at the bottom of a file but used throughout the reader will have to scroll around to find the definition rather than immediately seeing it at the top.

/*jshint immed: true */
function doStuff() {}
doStuff();

Note that this is an enforcing option which means JSHint does not apply it by default. If you do not explicitly set this option to true JSHint will allow references to appear before declarations.

Recommendation

Set this option to true (ensures declarations appear before references).