History

This warning has existed in two forms in JSHint and ESLint. It was introduced in the original version of JSLHnt and has remained in both tools since. It does not feature in JSLint.

• In JSHint the message used is "'with' is not allowed in strict mode"

• In ESLint the message has always been "Strict mode code may not include a with statement"

The situations that produce the warning have not changed despite changes to the text of the warning itself.

When do I get this error?

The "'with' is not allowed in strict mode" error, and the alternative "Strict mode code may not include a with statement", is thrown when JSHint or ESLint encounters the with statement in code that is running in strict mode. Here's an example:

function example() {
    "use strict";
    var a = {
        b: 10
    };
    with (a) {
        b = 20;
    }
}

Why do I get this error?

This error is raised to highlight a fatal JavaScript syntax error. Your code will fail to run in any environment that supports strict mode. The ECMAScript 5 specification clearly states that the presence of a with statement within strict mode code is illegal (ES5 §12.10.1):

Strict mode code may not include a WithStatement. The occurrence of a WithStatement in such a context is treated as a SyntaxError.

You can solve this problem by reworking code that uses with statements to fully qualify the "namespace". The following example will behave in exactly the same way as the first example above:

function example() {
    "use strict";
    var a = {
        b: 10
    };
    a.b = 20;
}

If you rely upon the behaviour of the with statement for a valid use-case, your only option is to ensure your code does not run in strict mode. This results in a different message from JSHint, but one that can be surpressed (in version 1.0.0 and above) with the appropriate warning identifier flag. See the page on the "Don't use with" error for more details:

function example() {
    var a = {
        b: 10
    };
    with (a) {
        b = 20;
    }
}

In JSHint 1.0.0 and above you have the ability to ignore any warning with a special option syntax. Since this message relates to a fatal syntax error you cannot disable it.