Function bind
has a Cognitive Complexity of 7 (exceeds 5 allowed). Consider refactoring. Open
Function.prototype.bind = function(oThis) {
if (typeof this !== 'function') {
// closest thing possible to the ECMAScript 5
// internal IsCallable function
throw new TypeError('Function.prototype.bind - what is trying to be bound is not callable');
- Read upRead up
Cognitive Complexity
Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.
A method's cognitive complexity is based on a few simple rules:
- Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
- Code is considered more complex for each "break in the linear flow of the code"
- Code is considered more complex when "flow breaking structures are nested"
Further reading
Function prototype is read only, properties should not be added. Open
Function.prototype.bind = function(oThis) {
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- Exclude checks
Disallow Extending of Native Objects (no-extend-native)
In JavaScript, you can extend any object, including builtin or "native" objects. Sometimes people change the behavior of these native objects in ways that break the assumptions made about them in other parts of the code.
For example here we are overriding a builtin method that will then affect all Objects, even other builtins.
// seems harmless
Object.prototype.extra = 55;
// loop through some userIds
var users = {
"123": "Stan",
"456": "David"
};
// not what you'd expect
for (var id in users) {
console.log(id); // "123", "456", "extra"
}
A common suggestion to avoid this problem would be to wrap the inside of the for
loop with users.hasOwnProperty(id)
. However, if this rule is strictly enforced throughout your codebase you won't need to take that step.
Rule Details
Disallows directly modifying the prototype of builtin objects.
Examples of incorrect code for this rule:
/*eslint no-extend-native: "error"*/
Object.prototype.a = "a";
Object.defineProperty(Array.prototype, "times", { value: 999 });
Options
This rule accepts an exceptions
option, which can be used to specify a list of builtins for which extensions will be allowed.
exceptions
Examples of correct code for the sample { "exceptions": ["Object"] }
option:
/*eslint no-extend-native: ["error", { "exceptions": ["Object"] }]*/
Object.prototype.a = "a";
Known Limitations
This rule does not report any of the following less obvious approaches to modify the prototype of builtin objects:
var x = Object;
x.prototype.thing = a;
eval("Array.prototype.forEach = 'muhahaha'");
with(Array) {
prototype.thing = 'thing';
};
window.Function.prototype.bind = 'tight';
When Not To Use It
You may want to disable this rule when working with polyfills that try to patch older versions of JavaScript with the latest spec, such as those that might Function.prototype.bind
or Array.prototype.forEach
in a future-friendly way.
Related Rules
- [no-global-assign](no-global-assign.md) Source: http://eslint.org/docs/rules/