.jshintignore

// --------------------------------------------------------------------
// WordPress JSHint Ignored
// --------------------------------------------------------------------
wp-admin/js/farbtastic.js
wp-admin/js/iris.min.js
wp-includes/js/crop/*
wp-includes/js/imgareaselect/*
wp-includes/js/jcrop/*
wp-includes/js/jquery/*
wp-includes/js/mediaelement/*
wp-includes/js/plupload/*
wp-includes/js/swfupload/*
wp-includes/js/thickbox/*
wp-includes/js/tinymce/*
wp-includes/js/colorpicker.js
wp-includes/js/hoverintent.js
wp-includes/js/json2.js
wp-includes/js/quicktags.js
wp-includes/js/swfobject.js
wp-includes/js/tw-sack.js

.jshintrc

// --------------------------------------------------------------------
// WordPress JSHint Configuration
// --------------------------------------------------------------------
{
    "bitwise"       : true,     // Prohibit bitwise operators (&, |, ^, etc.).
    "curly"         : true,     // Require {} for every new block or scope.
    "eqeqeq"        : true,     // Require triple equals i.e. `===`.
    "forin"         : true,     // Tolerate `for in` loops without `hasOwnPrototype`.
    "immed"         : true,     // Require immediate invocations to be wrapped in parens e.g. `( function(){}() );`
    "latedef"       : true,     // Prohibit variable use before definition.
    "newcap"        : true,     // Require capitalization of all constructor functions e.g. `new F()`.
    "noarg"         : true,     // Prohibit use of `arguments.caller` and `arguments.callee`.
    "noempty"       : true,     // Prohibit use of empty blocks.
    "nonew"         : true,     // Prohibit use of constructors for side-effects.
    "plusplus"      : false,    // Prohibit use of `++` & `--`.
    "regexp"        : false,    // Prohibit `.` and `[^...]` in regular expressions.
    "undef"         : true,     // Require all non-global variables be declared before they are used.
    "strict"        : true,     // Require `use strict` pragma in every file.
    "trailing"      : true,     // Prohibit trailing whitespaces.
    "asi"           : false,    // Tolerate Automatic Semicolon Insertion (no semicolons).
    "boss"          : false,    // Tolerate assignments inside if, for & while. Usually conditions & loops are for comparison, not assignments.
    "debug"         : false,    // Allow debugger statements e.g. browser breakpoints.
    "eqnull"        : false,    // Tolerate use of `== null`.
    "es5"           : false,    // Allow EcmaScript 5 syntax.
    "esnext"        : false,    // Allow ES.next specific features such as `const` and `let`.
    "evil"          : false,    // Tolerate use of `eval`.
    "expr"          : false,    // Tolerate `ExpressionStatement` as Programs.
    "funcscope"     : false,    // Tolerate declarations of variables inside of control structures while accessing them later from the outside.
    "globalstrict"  : false,    // Allow global "use strict" (also enables 'strict').
    "iterator"      : false,    // Allow usage of __iterator__ property.
    "lastsemic"     : false,    // Tolerate missing semicolons when it is omitted for the last statement in a one-line block.
    "laxbreak"      : false,    // Tolerate unsafe line breaks e.g. `return [\n] x` without semicolons.
    "laxcomma"      : false,    // Suppress warnings about comma-first coding style.
    "loopfunc"      : false,    // Allow functions to be defined within loops.
    "multistr"      : false,    // Tolerate multi-line strings.
    "onecase"       : false,    // Tolerate switches with just one case.
    "proto"         : false,    // Tolerate __proto__ property. This property is deprecated.
    "regexdash"     : false,    // Tolerate unescaped last dash i.e. `[-...]`.
    "scripturl"     : false,    // Tolerate script-targeted URLs.
    "smarttabs"     : false,    // Tolerate mixed tabs and spaces when the latter are used for alignmnent only.
    "shadow"        : false,    // Allows re-define variables later in code e.g. `var x=1; x=2;`.
    "sub"           : false,    // Tolerate all forms of subscript notation besides dot notation e.g. `dict['key']` instead of `dict.key`.
    "supernew"      : true,     // Tolerate `new function () { ... };` and `new Object;`.
    "validthis"     : false,    // Tolerate strict violations when the code is running in strict mode and you use this in a non-constructor function.
    "browser"       : true,     // Standard browser globals e.g. `window`, `document`.
    "couch"         : false,    // Enable globals exposed by CouchDB.
    "devel"         : false,    // Allow development statements e.g. `console.log();`.
    "dojo"          : false,    // Enable globals exposed by Dojo Toolkit.
    "jquery"        : true,     // Enable globals exposed by jQuery JavaScript library.
    "mootools"      : false,    // Enable globals exposed by MooTools JavaScript framework.
    "node"          : false,    // Enable globals available when code is running inside of the NodeJS runtime environment.
    "nonstandard"   : false,    // Define non-standard but widely adopted globals such as escape and unescape.
    "prototypejs"   : false,    // Enable globals exposed by Prototype JavaScript framework.
    "rhino"         : false,    // Enable globals available when your code is running inside of the Rhino runtime environment.
    "wsh"           : false,    // Enable globals available when your code is running as a script for the Windows Script Host.
    "nomen"         : false,    // Prohibit use of initial or trailing underbars in names.
    "onevar"        : false,    // Allow only one `var` statement per function.
    "passfail"      : false,    // Stop on first error.
    "white"         : false,    // Check against strict whitespace and indentation rules.
    "maxerr"        : 100,      // Maximum errors before stopping.
    "predef"        : [],       // Extra globals.
    "indent"        : 4         // Specify indentation spacing
}

The core codebase as-is does not consistently abide by "curly" for one-line statements -- see the media files, e.g.

I personally prefer my code this way, but that's one where I might have opted for the alternative in order to necessitate fewer changes to the core codebase for JSHint compliance.

Will review the rest ASAP.

Can you highlight which values are defaults, or which are not? Perhaps move the changed values to the top, then a clear linespace before the default values.

re: curly and other bits - could this be a three-step change?

1. Get .jshintrc added, with whatever values currently matches the existing code.
2. Identify and agree which of the remaining values we'd like the code to meet (curly, onevar, white, for a troll-ish example).
3. Work on patches that change those values and tighten's the existing code to match them.

onevar is noted as a legacy option on JSHint's docs, iirc, so while we can use it if we agree to it may go away