Showing 51 of 51 total issues
Do not access Object.prototype method 'hasOwnProperty' from target object. Open
} else if (t.isIdentifier(expr) && context.hasOwnProperty(expr.name)) {
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- Exclude checks
Disallow use of Object.prototypes builtins directly (no-prototype-builtins)
In ECMAScript 5.1, Object.create
was added, which enables the creation of objects with a specified [[Prototype]]
. Object.create(null)
is a common pattern used to create objects that will be used as a Map. This can lead to errors when it is assumed that objects will have properties from Object.prototype
. This rule prevents calling Object.prototype
methods directly from an object.
Rule Details
This rule disallows calling some Object.prototype
methods directly on object instances.
Examples of incorrect code for this rule:
/*eslint no-prototype-builtins: "error"*/
var hasBarProperty = foo.hasOwnProperty("bar");
var isPrototypeOfBar = foo.isPrototypeOf(bar);
var barIsEnumerable = foo.propertyIsEnumerable("bar");
Examples of correct code for this rule:
/*eslint no-prototype-builtins: "error"*/
var hasBarProperty = Object.prototype.hasOwnProperty.call(foo, "bar");
var isPrototypeOfBar = Object.prototype.isPrototypeOf.call(foo, bar);
var barIsEnumerable = {}.propertyIsEnumerable.call(foo, "bar");
When Not To Use It
You may want to turn this rule off if you will never use an object that shadows an Object.prototype
method or which does not inherit from Object.prototype
.
Source: http://eslint.org/docs/rules/
Missing trailing comma. Open
)
- Read upRead up
- Exclude checks
require or disallow trailing commas (comma-dangle)
Trailing commas in object literals are valid according to the ECMAScript 5 (and ECMAScript 3!) spec. However, IE8 (when not in IE8 document mode) and below will throw an error when it encounters trailing commas in JavaScript.
var foo = {
bar: "baz",
qux: "quux",
};
Trailing commas simplify adding and removing items to objects and arrays, since only the lines you are modifying must be touched. Another argument in favor of trailing commas is that it improves the clarity of diffs when an item is added or removed from an object or array:
Less clear:
var foo = {
- bar: "baz",
- qux: "quux"
+ bar: "baz"
};
More clear:
var foo = {
bar: "baz",
- qux: "quux",
};
Rule Details
This rule enforces consistent use of trailing commas in object and array literals.
Options
This rule has a string option or an object option:
{
"comma-dangle": ["error", "never"],
// or
"comma-dangle": ["error", {
"arrays": "never",
"objects": "never",
"imports": "never",
"exports": "never",
"functions": "ignore",
}]
}
-
"never"
(default) disallows trailing commas -
"always"
requires trailing commas -
"always-multiline"
requires trailing commas when the last element or property is in a different line than the closing]
or}
and disallows trailing commas when the last element or property is on the same line as the closing]
or}
-
"only-multiline"
allows (but does not require) trailing commas when the last element or property is in a different line than the closing]
or}
and disallows trailing commas when the last element or property is on the same line as the closing]
or}
Trailing commas in function declarations and function calls are valid syntax since ECMAScript 2017; however, the string option does not check these situations for backwards compatibility.
You can also use an object option to configure this rule for each type of syntax.
Each of the following options can be set to "never"
, "always"
, "always-multiline"
, "only-multiline"
, or "ignore"
.
The default for each option is "never"
unless otherwise specified.
-
arrays
is for array literals and array patterns of destructuring. (e.g.let [a,] = [1,];
) -
objects
is for object literals and object patterns of destructuring. (e.g.let {a,} = {a: 1};
) -
imports
is for import declarations of ES Modules. (e.g.import {a,} from "foo";
) -
exports
is for export declarations of ES Modules. (e.g.export {a,};
) -
functions
is for function declarations and function calls. (e.g.(function(a,){ })(b,);
)
functions
is set to"ignore"
by default for consistency with the string option.
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint comma-dangle: ["error", "never"]*/
var foo = {
bar: "baz",
qux: "quux",
};
var arr = [1,2,];
foo({
bar: "baz",
qux: "quux",
});
Examples of correct code for this rule with the default "never"
option:
/*eslint comma-dangle: ["error", "never"]*/
var foo = {
bar: "baz",
qux: "quux"
};
var arr = [1,2];
foo({
bar: "baz",
qux: "quux"
});
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint comma-dangle: ["error", "always"]*/
var foo = {
bar: "baz",
qux: "quux"
};
var arr = [1,2];
foo({
bar: "baz",
qux: "quux"
});
Examples of correct code for this rule with the "always"
option:
/*eslint comma-dangle: ["error", "always"]*/
var foo = {
bar: "baz",
qux: "quux",
};
var arr = [1,2,];
foo({
bar: "baz",
qux: "quux",
});
always-multiline
Examples of incorrect code for this rule with the "always-multiline"
option:
/*eslint comma-dangle: ["error", "always-multiline"]*/
var foo = {
bar: "baz",
qux: "quux"
};
var foo = { bar: "baz", qux: "quux", };
var arr = [1,2,];
var arr = [1,
2,];
var arr = [
1,
2
];
foo({
bar: "baz",
qux: "quux"
});
Examples of correct code for this rule with the "always-multiline"
option:
/*eslint comma-dangle: ["error", "always-multiline"]*/
var foo = {
bar: "baz",
qux: "quux",
};
var foo = {bar: "baz", qux: "quux"};
var arr = [1,2];
var arr = [1,
2];
var arr = [
1,
2,
];
foo({
bar: "baz",
qux: "quux",
});
only-multiline
Examples of incorrect code for this rule with the "only-multiline"
option:
/*eslint comma-dangle: ["error", "only-multiline"]*/
var foo = { bar: "baz", qux: "quux", };
var arr = [1,2,];
var arr = [1,
2,];
Examples of correct code for this rule with the "only-multiline"
option:
/*eslint comma-dangle: ["error", "only-multiline"]*/
var foo = {
bar: "baz",
qux: "quux",
};
var foo = {
bar: "baz",
qux: "quux"
};
var foo = {bar: "baz", qux: "quux"};
var arr = [1,2];
var arr = [1,
2];
var arr = [
1,
2,
];
var arr = [
1,
2
];
foo({
bar: "baz",
qux: "quux",
});
foo({
bar: "baz",
qux: "quux"
});
functions
Examples of incorrect code for this rule with the {"functions": "never"}
option:
/*eslint comma-dangle: ["error", {"functions": "never"}]*/
function foo(a, b,) {
}
foo(a, b,);
new foo(a, b,);
Examples of correct code for this rule with the {"functions": "never"}
option:
/*eslint comma-dangle: ["error", {"functions": "never"}]*/
function foo(a, b) {
}
foo(a, b);
new foo(a, b);
Examples of incorrect code for this rule with the {"functions": "always"}
option:
/*eslint comma-dangle: ["error", {"functions": "always"}]*/
function foo(a, b) {
}
foo(a, b);
new foo(a, b);
Examples of correct code for this rule with the {"functions": "always"}
option:
/*eslint comma-dangle: ["error", {"functions": "always"}]*/
function foo(a, b,) {
}
foo(a, b,);
new foo(a, b,);
When Not To Use It
You can turn this rule off if you are not concerned with dangling commas. Source: http://eslint.org/docs/rules/
Unexpected string concatenation. Open
return '_' + keys.length.toString(36).split('').reverse().join('');
- Read upRead up
- Exclude checks
Suggest using template literals instead of string concatenation. (prefer-template)
In ES2015 (ES6), we can use template literals instead of string concatenation.
var str = "Hello, " + name + "!";
/*eslint-env es6*/
var str = `Hello, ${name}!`;
Rule Details
This rule is aimed to flag usage of +
operators with strings.
Examples
Examples of incorrect code for this rule:
/*eslint prefer-template: "error"*/
var str = "Hello, " + name + "!";
var str = "Time: " + (12 * 60 * 60 * 1000);
Examples of correct code for this rule:
/*eslint prefer-template: "error"*/
/*eslint-env es6*/
var str = "Hello World!";
var str = `Hello, ${name}!`;
var str = `Time: ${12 * 60 * 60 * 1000}`;
// This is reported by `no-useless-concat`.
var str = "Hello, " + "World!";
When Not To Use It
This rule should not be used in ES3/5 environments.
In ES2015 (ES6) or later, if you don't want to be notified about string concatenation, you can safely disable this rule.
Related Rules
- [no-useless-concat](no-useless-concat.md)
- [quotes](quotes.md) Source: http://eslint.org/docs/rules/
Unnecessary escape character: [. Open
const hasAttachedSelector = /[^:\[]+[:\[]/;
- Read upRead up
- Exclude checks
Disallow unnecessary escape usage (no-useless-escape)
Escaping non-special characters in strings, template literals, and regular expressions doesn't have any effect, as demonstrated in the following example:
let foo = "hol\a"; // > foo = "hola"
let bar = `${foo}\!`; // > bar = "hola!"
let baz = /\:/ // same functionality with /:/
Rule Details
This rule flags escapes that can be safely removed without changing behavior.
Examples of incorrect code for this rule:
/*eslint no-useless-escape: "error"*/
"\'";
'\"';
"\#";
"\e";
`\"`;
`\"${foo}\"`;
`\#{foo}`;
/\!/;
/\@/;
Examples of correct code for this rule:
/*eslint no-useless-escape: "error"*/
"\"";
'\'';
"\x12";
"\u00a9";
"\371";
"xs\u2111";
`\``;
`\${${foo}\}`;
`$\{${foo}\}`;
/\\/g;
/\t/g;
/\w\$\*\^\./;
When Not To Use It
If you don't want to be notified about unnecessary escapes, you can safely disable this rule. Source: http://eslint.org/docs/rules/
Unexpected string concatenation. Open
this.filePath = path.resolve(path.join(options.cacheDir, 'babel-plugin-css-in-js', name + '.json'));
- Read upRead up
- Exclude checks
Suggest using template literals instead of string concatenation. (prefer-template)
In ES2015 (ES6), we can use template literals instead of string concatenation.
var str = "Hello, " + name + "!";
/*eslint-env es6*/
var str = `Hello, ${name}!`;
Rule Details
This rule is aimed to flag usage of +
operators with strings.
Examples
Examples of incorrect code for this rule:
/*eslint prefer-template: "error"*/
var str = "Hello, " + name + "!";
var str = "Time: " + (12 * 60 * 60 * 1000);
Examples of correct code for this rule:
/*eslint prefer-template: "error"*/
/*eslint-env es6*/
var str = "Hello World!";
var str = `Hello, ${name}!`;
var str = `Time: ${12 * 60 * 60 * 1000}`;
// This is reported by `no-useless-concat`.
var str = "Hello, " + "World!";
When Not To Use It
This rule should not be used in ES3/5 environments.
In ES2015 (ES6) or later, if you don't want to be notified about string concatenation, you can safely disable this rule.
Related Rules
- [no-useless-concat](no-useless-concat.md)
- [quotes](quotes.md) Source: http://eslint.org/docs/rules/
Unexpected string concatenation. Open
result += options.prefixes.map(p => p.replace(invalidChars, '_')).join('-') + '-';
- Read upRead up
- Exclude checks
Suggest using template literals instead of string concatenation. (prefer-template)
In ES2015 (ES6), we can use template literals instead of string concatenation.
var str = "Hello, " + name + "!";
/*eslint-env es6*/
var str = `Hello, ${name}!`;
Rule Details
This rule is aimed to flag usage of +
operators with strings.
Examples
Examples of incorrect code for this rule:
/*eslint prefer-template: "error"*/
var str = "Hello, " + name + "!";
var str = "Time: " + (12 * 60 * 60 * 1000);
Examples of correct code for this rule:
/*eslint prefer-template: "error"*/
/*eslint-env es6*/
var str = "Hello World!";
var str = `Hello, ${name}!`;
var str = `Time: ${12 * 60 * 60 * 1000}`;
// This is reported by `no-useless-concat`.
var str = "Hello, " + "World!";
When Not To Use It
This rule should not be used in ES3/5 environments.
In ES2015 (ES6) or later, if you don't want to be notified about string concatenation, you can safely disable this rule.
Related Rules
- [no-useless-concat](no-useless-concat.md)
- [quotes](quotes.md) Source: http://eslint.org/docs/rules/
Unexpected string concatenation. Open
value = '' + value + 'px';
- Read upRead up
- Exclude checks
Suggest using template literals instead of string concatenation. (prefer-template)
In ES2015 (ES6), we can use template literals instead of string concatenation.
var str = "Hello, " + name + "!";
/*eslint-env es6*/
var str = `Hello, ${name}!`;
Rule Details
This rule is aimed to flag usage of +
operators with strings.
Examples
Examples of incorrect code for this rule:
/*eslint prefer-template: "error"*/
var str = "Hello, " + name + "!";
var str = "Time: " + (12 * 60 * 60 * 1000);
Examples of correct code for this rule:
/*eslint prefer-template: "error"*/
/*eslint-env es6*/
var str = "Hello World!";
var str = `Hello, ${name}!`;
var str = `Time: ${12 * 60 * 60 * 1000}`;
// This is reported by `no-useless-concat`.
var str = "Hello, " + "World!";
When Not To Use It
This rule should not be used in ES3/5 environments.
In ES2015 (ES6) or later, if you don't want to be notified about string concatenation, you can safely disable this rule.
Related Rules
- [no-useless-concat](no-useless-concat.md)
- [quotes](quotes.md) Source: http://eslint.org/docs/rules/
Calls to require() should use string literals Open
contextFileCache[file] = require(file);
- Read upRead up
- Exclude checks
For more information visit Source: http://eslint.org/docs/rules/
Unexpected string concatenation. Open
css.push(indent(level) + selector + ' {');
- Read upRead up
- Exclude checks
Suggest using template literals instead of string concatenation. (prefer-template)
In ES2015 (ES6), we can use template literals instead of string concatenation.
var str = "Hello, " + name + "!";
/*eslint-env es6*/
var str = `Hello, ${name}!`;
Rule Details
This rule is aimed to flag usage of +
operators with strings.
Examples
Examples of incorrect code for this rule:
/*eslint prefer-template: "error"*/
var str = "Hello, " + name + "!";
var str = "Time: " + (12 * 60 * 60 * 1000);
Examples of correct code for this rule:
/*eslint prefer-template: "error"*/
/*eslint-env es6*/
var str = "Hello World!";
var str = `Hello, ${name}!`;
var str = `Time: ${12 * 60 * 60 * 1000}`;
// This is reported by `no-useless-concat`.
var str = "Hello, " + "World!";
When Not To Use It
This rule should not be used in ES3/5 environments.
In ES2015 (ES6) or later, if you don't want to be notified about string concatenation, you can safely disable this rule.
Related Rules
- [no-useless-concat](no-useless-concat.md)
- [quotes](quotes.md) Source: http://eslint.org/docs/rules/
Unexpected string concatenation. Open
result += options.prefix.replace(invalidChars, '_') + '-';
- Read upRead up
- Exclude checks
Suggest using template literals instead of string concatenation. (prefer-template)
In ES2015 (ES6), we can use template literals instead of string concatenation.
var str = "Hello, " + name + "!";
/*eslint-env es6*/
var str = `Hello, ${name}!`;
Rule Details
This rule is aimed to flag usage of +
operators with strings.
Examples
Examples of incorrect code for this rule:
/*eslint prefer-template: "error"*/
var str = "Hello, " + name + "!";
var str = "Time: " + (12 * 60 * 60 * 1000);
Examples of correct code for this rule:
/*eslint prefer-template: "error"*/
/*eslint-env es6*/
var str = "Hello World!";
var str = `Hello, ${name}!`;
var str = `Time: ${12 * 60 * 60 * 1000}`;
// This is reported by `no-useless-concat`.
var str = "Hello, " + "World!";
When Not To Use It
This rule should not be used in ES3/5 environments.
In ES2015 (ES6) or later, if you don't want to be notified about string concatenation, you can safely disable this rule.
Related Rules
- [no-useless-concat](no-useless-concat.md)
- [quotes](quotes.md) Source: http://eslint.org/docs/rules/
Missing trailing comma. Open
'must be a function expression'
- Read upRead up
- Exclude checks
require or disallow trailing commas (comma-dangle)
Trailing commas in object literals are valid according to the ECMAScript 5 (and ECMAScript 3!) spec. However, IE8 (when not in IE8 document mode) and below will throw an error when it encounters trailing commas in JavaScript.
var foo = {
bar: "baz",
qux: "quux",
};
Trailing commas simplify adding and removing items to objects and arrays, since only the lines you are modifying must be touched. Another argument in favor of trailing commas is that it improves the clarity of diffs when an item is added or removed from an object or array:
Less clear:
var foo = {
- bar: "baz",
- qux: "quux"
+ bar: "baz"
};
More clear:
var foo = {
bar: "baz",
- qux: "quux",
};
Rule Details
This rule enforces consistent use of trailing commas in object and array literals.
Options
This rule has a string option or an object option:
{
"comma-dangle": ["error", "never"],
// or
"comma-dangle": ["error", {
"arrays": "never",
"objects": "never",
"imports": "never",
"exports": "never",
"functions": "ignore",
}]
}
-
"never"
(default) disallows trailing commas -
"always"
requires trailing commas -
"always-multiline"
requires trailing commas when the last element or property is in a different line than the closing]
or}
and disallows trailing commas when the last element or property is on the same line as the closing]
or}
-
"only-multiline"
allows (but does not require) trailing commas when the last element or property is in a different line than the closing]
or}
and disallows trailing commas when the last element or property is on the same line as the closing]
or}
Trailing commas in function declarations and function calls are valid syntax since ECMAScript 2017; however, the string option does not check these situations for backwards compatibility.
You can also use an object option to configure this rule for each type of syntax.
Each of the following options can be set to "never"
, "always"
, "always-multiline"
, "only-multiline"
, or "ignore"
.
The default for each option is "never"
unless otherwise specified.
-
arrays
is for array literals and array patterns of destructuring. (e.g.let [a,] = [1,];
) -
objects
is for object literals and object patterns of destructuring. (e.g.let {a,} = {a: 1};
) -
imports
is for import declarations of ES Modules. (e.g.import {a,} from "foo";
) -
exports
is for export declarations of ES Modules. (e.g.export {a,};
) -
functions
is for function declarations and function calls. (e.g.(function(a,){ })(b,);
)
functions
is set to"ignore"
by default for consistency with the string option.
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint comma-dangle: ["error", "never"]*/
var foo = {
bar: "baz",
qux: "quux",
};
var arr = [1,2,];
foo({
bar: "baz",
qux: "quux",
});
Examples of correct code for this rule with the default "never"
option:
/*eslint comma-dangle: ["error", "never"]*/
var foo = {
bar: "baz",
qux: "quux"
};
var arr = [1,2];
foo({
bar: "baz",
qux: "quux"
});
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint comma-dangle: ["error", "always"]*/
var foo = {
bar: "baz",
qux: "quux"
};
var arr = [1,2];
foo({
bar: "baz",
qux: "quux"
});
Examples of correct code for this rule with the "always"
option:
/*eslint comma-dangle: ["error", "always"]*/
var foo = {
bar: "baz",
qux: "quux",
};
var arr = [1,2,];
foo({
bar: "baz",
qux: "quux",
});
always-multiline
Examples of incorrect code for this rule with the "always-multiline"
option:
/*eslint comma-dangle: ["error", "always-multiline"]*/
var foo = {
bar: "baz",
qux: "quux"
};
var foo = { bar: "baz", qux: "quux", };
var arr = [1,2,];
var arr = [1,
2,];
var arr = [
1,
2
];
foo({
bar: "baz",
qux: "quux"
});
Examples of correct code for this rule with the "always-multiline"
option:
/*eslint comma-dangle: ["error", "always-multiline"]*/
var foo = {
bar: "baz",
qux: "quux",
};
var foo = {bar: "baz", qux: "quux"};
var arr = [1,2];
var arr = [1,
2];
var arr = [
1,
2,
];
foo({
bar: "baz",
qux: "quux",
});
only-multiline
Examples of incorrect code for this rule with the "only-multiline"
option:
/*eslint comma-dangle: ["error", "only-multiline"]*/
var foo = { bar: "baz", qux: "quux", };
var arr = [1,2,];
var arr = [1,
2,];
Examples of correct code for this rule with the "only-multiline"
option:
/*eslint comma-dangle: ["error", "only-multiline"]*/
var foo = {
bar: "baz",
qux: "quux",
};
var foo = {
bar: "baz",
qux: "quux"
};
var foo = {bar: "baz", qux: "quux"};
var arr = [1,2];
var arr = [1,
2];
var arr = [
1,
2,
];
var arr = [
1,
2
];
foo({
bar: "baz",
qux: "quux",
});
foo({
bar: "baz",
qux: "quux"
});
functions
Examples of incorrect code for this rule with the {"functions": "never"}
option:
/*eslint comma-dangle: ["error", {"functions": "never"}]*/
function foo(a, b,) {
}
foo(a, b,);
new foo(a, b,);
Examples of correct code for this rule with the {"functions": "never"}
option:
/*eslint comma-dangle: ["error", {"functions": "never"}]*/
function foo(a, b) {
}
foo(a, b);
new foo(a, b);
Examples of incorrect code for this rule with the {"functions": "always"}
option:
/*eslint comma-dangle: ["error", {"functions": "always"}]*/
function foo(a, b) {
}
foo(a, b);
new foo(a, b);
Examples of correct code for this rule with the {"functions": "always"}
option:
/*eslint comma-dangle: ["error", {"functions": "always"}]*/
function foo(a, b,) {
}
foo(a, b,);
new foo(a, b,);
When Not To Use It
You can turn this rule off if you are not concerned with dangling commas. Source: http://eslint.org/docs/rules/