no-throw-literal

Disallow throwing literals as exceptions

It is considered good practice to only throw the Error object itself or an object using the Error object as base objects for user-defined exceptions. The fundamental benefit of Error objects is that they automatically keep track of where they were built and originated.

This rule restricts what can be thrown as an exception. When it was first created, it only prevented literals from being thrown (hence the name), but it has now been expanded to only allow expressions which have a possibility of being an Error object.

Rule Details

This rule is aimed at maintaining consistency when throwing exception by disallowing to throw literals and other expressions which cannot possibly be an Error object.

Examples of incorrect code for this rule:

/*eslint no-throw-literal: "error"*/
/*eslint-env es6*/

throw "error";

throw 0;

throw undefined;

throw null;

var err = new Error();
throw "an " + err;
// err is recast to a string literal

var err = new Error();
throw `${err}`

Examples of correct code for this rule:

/*eslint no-throw-literal: "error"*/

throw new Error();

throw new Error("error");

var e = new Error("error");
throw e;

try {
    throw new Error("error");
} catch (e) {
    throw e;
}

Known Limitations

Due to the limits of static analysis, this rule cannot guarantee that you will only throw Error objects.

Examples of correct code for this rule, but which do not throw an Error object:

/*eslint no-throw-literal: "error"*/

var err = "error";
throw err;

function foo(bar) {
    console.log(bar);
}
throw foo("error");

throw new String("error");

var foo = {
    bar: "error"
};
throw foo.bar;

Version

This rule was introduced in ESLint v0.15.0.

Resources

• Rule source
• Tests source