Rule Suggestion: Prefer Arrow Callback

A rule for ES6 to recommend use of arrow functions in callback

Warnings when Arrow function is preferred

func( function () {...} )
setTimeout(function () {...}, 3000);

Not Warnings when Arrow function is preferred

func( () => {...} )
setTimeout( () => {...}, 3000);

Warnings when standard es5 function is preferred

func( () => {...} )
setTimeout( () => {...}, 3000);

Not Warnings when standard es5 function is preferred

func( function () {...} )
setTimeout(function () {...}, 3000);

Rule Example

"prefer-arrow-callback": [2, "always"]

or rule could alternatively look like:

"callback-style": [2, "arrow"]

ref conversation in #3113

[pigulla]

I think it would be a good idea to add an option to this to only enforce arrow functions for single expressions (i.e., like lambdas in Python).

"prefer-arrow-callback": [2, "except-mutliple-statements"]

With that option set, these would be considered warnings:

foo.forEach(function (item) { return item.toString(); });
foo.forEach(item => { item.bar(); return item.toString(); });

and these would be okay:

foo.forEach(item => item.toString());
foo.forEach(function (item) { item.bar(); return item.toString(); });

[ilyavolodin]

@mysticatea I don’t think so. Let’s hold of on opposite style until somebody requests it.