Add "variables" option to `no-use-before-define` rule

• ESLint Version: 3.5.0

I want no-use-before-define to check for classes or functions that are used before they are defined. But I do not want to check for variables that are used before they are defined.

Right now there exist two options, which modify whether functions and classes are checked. For example, I can disable these two checks:

"no-use-before-define": [2, { "functions": false, "classes": false }]

But I cannot disable checking if variables are used before they are defined. I propose adding a “variables” option to address this:

"no-use-before-define": [2, { "variables": false }]

There is already a precedent for an option like this, in the “blocks” option to the padded-blocks rule. It’s used like this:

"padded-blocks": [2, { "blocks": "never", "switches": "never", "classes": "never" }]

[feross]

I’m not opposed, but I’d love to see a real-world case where this is a problem (especially if it’s something that “standard” recommends but cannot enforce, or wants to recommend but cannot, due to this limitation).

In standard, we would like to prevent clearly incorrect use-before-define cases like the following:

console.log(foo);
var foo = 5;

While still allowing cases that may be correct if the program executes in the right order:

function printFoo() {
     // Variable "foo" is not used before it is defined, even though it
     // appears in the source before foo is defined.
    console.log(foo);
}
var foo = 5;
printFoo();

There are just too many false positives for us when the latter example is disallowed.

[not-an-aardvark]

PR up at https://github.com/eslint/eslint/issues/7948