no-global-assign

Disallow assignments to native objects or read-only global variables

JavaScript environments contain a number of built-in global variables, such as window in browsers and process in Node.js. In almost all cases, you don’t want to assign a value to these global variables as doing so could result in losing access to important functionality. For example, you probably don’t want to do this in browser code:

window = {}; 
1

While examples such as window are obvious, there are often hundreds of built-in global objects provided by JavaScript environments. It can be hard to know if you’re assigning to a global variable or not.

Rule Details

This rule disallows modifications to read-only global variables.

ESLint has the capability to configure global variables as read-only.

See also: Specifying Globals

Examples of incorrect code for this rule:

/*eslint no-global-assign: "error"*/ Object = null undefined = 1 
1
2
3
4

/*eslint no-global-assign: "error"*/ /*global window:readonly*/ window = {} 
1
2
3
4

Examples of correct code for this rule:

/*eslint no-global-assign: "error"*/ a = 1 let b = 1 b = 2 
1
2
3
4
5

/*eslint no-global-assign: "error"*/ /*global onload:writable*/ onload = function() {} 
1
2
3
4

Options

This rule accepts an exceptions option, which can be used to specify a list of builtins for which reassignments will be allowed:

{ "rules": { "no-global-assign": ["error", {"exceptions": ["Object"]}] } } 
1
2
3
4
5

When Not To Use It

If you are trying to override one of the native objects.

Related Rules

• no-extend-native
• no-redeclare
• no-shadow

Version

This rule was introduced in ESLint v3.3.0.

Resources

• Rule source
• Tests source