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Add rules for prohibiting unused vars/expressions #78

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Add rules for prohibiting unused vars/expressions #78

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Add rules for prohibiting unused vars/expressions
haroldtreen Nov 14, 2015
828e510
Merge branch 'master' into unused-vars
Jan 18, 2016
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6 changes: 5 additions & 1 deletion javascript/.eslintrc
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Original file line number Diff line number Diff line change
Expand Up @@ -110,6 +110,10 @@
"semi": 2,

// Disallow function definitions of the form 'function myFunc() {'
"func-style": [2, "expression"]
"func-style": [2, "expression"],

// Disallow unused variables/expressions
"no-unused-vars": 2,
"no-unused-expressions": 2
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I would suggest to allow the use of short circuits and ternary conditionals, since I see those a lot.

"no-unused-expressions": [2, { allowShortCircuit: true, allowTernary: true }]

}
}
15 changes: 15 additions & 0 deletions javascript/README.md
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Expand Up @@ -88,6 +88,21 @@ var length = items.length;
var name = 'foo';
````

## Don't have unused variables/expressions
```javascript
// Bad: Many of these variables/expressions are useless
{} // object - not used
var newArray = []; // newArray - not used
['1', '2', '3', '4'].forEach(function(num, index) { // index - not used
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What about when something you need is in the second argument? Say we wanted index but not num - a functional programming common practice is to use _ in it's place, but will the linter complain about that? If so I don't think we should add it to the linting rules.

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@jansepar There are options to eslint we can use to ignore unused arguments to functions. That seems like it'd be a pragmatic compromise here.

"no-unused-vars": [2, {"vars": "all", "args": "none" }]

Reference: https://github.com/eslint/eslint/blob/master/docs/rules/no-unused-vars.md

Interestingly, I have no idea what the 2 is for in the array. All examples used 2 and the docs don't say what it's for. 😕

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@jeremywiebe The 2 indicates that a rule violation will surface an error (exit code of 1) instead of just a warning.

http://eslint.org/docs/user-guide/configuring#configuring-rules

return num++;
});

// Good: Delete things you no longer need
['1', '2', '3', '4'].forEach(function(num) {
return num++;
});
```

##Use semi-colons

There are many more ways that things can break *without* semi-colons than *with* semi-colons.
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