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.

• Specifying Environments
• 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
var 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