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possibleErrors.md

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Possible Errors

Rule Description Snippet ESLint Default Link
comma-dangle Disallow or enforce trailing commas 
 var foo = {
    bar: "baz",
    qux: "quux",
};
Error [Link](http://eslint.org/docs/rules/comma-dangle)
no-cond-assign Disallow assignment in conditional expressions 
// Check the user's job title
if (user.jobTitle = "manager") {
    // user.jobTitle is now incorrect
}
Error except enclosed in extra parentheses [Link](http://eslint.org/docs/rules/no-cond-assign)
no-console Disallow use of console in the node environment 
console.log("Made it here.");
console.error("That shouldn't have happened.");
Error [Link](http://eslint.org/docs/rules/no-console)
no-constant-condition Disallow use of constant expressions in conditions 
if (false) {
    doSomethingUnfinished();
}
Error [Link](http://eslint.org/docs/rules/no-constant-condition)
no-control-regex Disallow control characters in regular expressions 
var pattern1 = /\\x1f/;
var pattern2 = new RegExp("\x1f");
Error [Link](http://eslint.org/docs/rules/no-control-regex)
no-debugger Disallow use of debugger 
debugger;
Error [Link](http://eslint.org/docs/rules/no-debugger)
no-dupe-args Disallow duplicate arguments in functions 
function (a, b, a) {
    console.log("which a is it?", a);
}
Error [Link](http://eslint.org/docs/rules/no-dupe-args)
no-dupe-keys Disallow duplicate keys when creation object literals 
var foo = {
    bar: "baz",
    bar: "qux"
};
Error [Link](http://eslint.org/docs/rules/no-dupe-keys)
no-duplicate-case Disallow a duplicate case label 
var a = 1;

switch (a) {
case 1:
break;
case 2:
break;
case 1:         // duplicate literal 1
break;
default:
break;
}

Error [Link](http://eslint.org/docs/rules/no-duplicate-case)
no-empty-character-class Disallow the use of empty character classes in regular expressions 
var foo = /^abc[]/;
Error [Link](http://eslint.org/docs/rules/no-empty-character-class)
no-empty Disallow empty statements 
if (foo) {
}
Error [Link](http://eslint.org/docs/rules/no-empty)
no-ex-assign Disallow assigning to the exception in a catch block 
try {
    // code
} catch (e) {
    e = 10;
}
Error [Link](http://eslint.org/docs/rules/no-ex-assign)
no-extra-boolean-cast Disallow double-negation boolean casts in a boolean context 
if (!!foo) {
    // ...
}
Error [Link](http://eslint.org/docs/rules/no-extra-boolean-cast)
no-extra-parens Disallow unecessary parentheses 
a = (b * c)
(a * b) + c
typeof (a)
Off [Link](http://eslint.org/docs/rules/no-extra-parens)
no-extra-semi Disallow unnecessary semicolons 
var x = 5;;
Error [Link](http://eslint.org/docs/rules/no-extra-semi)
no-func-assign Disallow overwriting functions written as function declarations 
function foo() {}
foo = bar;
Error [Link](http://eslint.org/docs/rules/no-func-assign)
no-inner-declarations Disallow function or variable declarations in nested blocks 
if (test) {
    function doSomethingElse () { }
}

function anotherThing() {
var fn;
if (test) {
// Good
fn = function expression() { };
// Bad
function declaration() { }
}
}

Error in functions [Link](http://eslint.org/docs/rules/no-inner-declarations)
no-invalid-regexp Disallow invalid regular expression strings in the RegExp constructor 
RegExp('['])
RegExp('.', 'z') // invalid flags
new RegExp('\\')
Error [Link](http://eslint.org/docs/rules/no-invalid-regexp)
no-irregular-whitespace Disallow irregular whitespace outside of strings and comments 
function thing(){  return 'test'; }
function thing(){  return 'test'; }
function thing(){  return 'test'; }
function thing(){  return 'test'; }
function thing() {  return 'test'; }
function thing() {  return 'test'; }
Error [Link](http://eslint.org/docs/rules/no-irregular-whitespace)
no-negated-in-lhs Disallow negation of the left operand of an in expression 
// Bad
if(!a in b) // do something
// Good
if(('' + !a) in b) // do something
Error [Link](http://eslint.org/docs/rules/no-negated-in-lhs)
no-obj-calls Disallow the use of object properties of the global object (Math and JSON) as functions 
var x = Math();
var y = JSON();
Error [Link](http://eslint.org/docs/rules/no-obj-calls)
no-regex-spaces Disallow multiple spaces in a regular expression literal 
// Bad
var re = /foo   bar/;
// Good
var re = /foo {3}bar/;
Error [Link](http://eslint.org/docs/rules/no-regex-spaces)
no-sparse-arrays Disallow sparse arrays 
var colors = [ "red",, "blue" ];
Error [Link](http://eslint.org/docs/rules/no-sparse-arrays)
no-unreachable Disallow uinreachable statements after a return, throw, continue, or break statement 
function fn() {
    x = 1;
    return x;
    x = 3; // this will never execute
}
Error [Link](http://eslint.org/docs/rules/no-unreachable)
use-isnan Disallow comparisons with the value NaN 
if (foo == NaN) {
    // ...
}
if (foo != NaN) {
    // ...
}
Error [Link](http://eslint.org/docs/rules/use-isnan)
valid-jsdoc Ensure JSDoc comments are valid 
// Good
/**
 * Adds two numbers together.
 * @param {int} num1 The first number.
 * @param {int} num2 The second number.
 * @returns {int} The sum of the two numbers.
 */
function sum(num1, num2) {
    return num1 + num2;
}
Off [Link](http://eslint.org/docs/rules/valid-jsdoc)
valid-typeof Ensure that the results of typeof are compared against a valid string 
typeof foo === "strnig"
typeof foo == "undefimed"
typeof bar != "nunber"
typeof bar !== "fucntion"
Error [Link](http://eslint.org/docs/rules/valid-typeof)
no-unexpected-multiline Avoid code that looks like two expressions but is actually one 
var foo = bar
(1 || 2).baz();

var hello = 'world'
[1, 2, 3].forEach(addNumber);

Off [Link](http://eslint.org/docs/rules/no-unexpected-multiline)