Disallow eval() (no-eval)

JavaScript's eval() function is potentially dangerous and is often misused. Using eval() on untrusted code can open a program up to several different injection attacks. The use of eval() in most contexts can be substituted for a better, alternative approach to a problem.

var obj = { x: "foo" },
    key = "x",
    value = eval("obj." + key);

Rule Details

This rule is aimed at preventing potentially dangerous, unnecessary, and slow code by disallowing the use of the eval() function. As such, it will warn whenever the eval() function is used.

Examples of incorrect code for this rule:

/*eslint no-eval: "error"*/

var obj = { x: "foo" },
    key = "x",
    value = eval("obj." + key);

(0, eval)("var a = 0");

var foo = eval;
foo("var a = 0");

// This `this` is the global object.
this.eval("var a = 0");

Example of additional incorrect code for this rule when browser environment is set to true:

/*eslint no-eval: "error"*/
/*eslint-env browser*/

window.eval("var a = 0");

Example of additional incorrect code for this rule when node environment is set to true:

/*eslint no-eval: "error"*/
/*eslint-env node*/

global.eval("var a = 0");

Examples of correct code for this rule:

/*eslint no-eval: "error"*/
/*eslint-env es6*/

var obj = { x: "foo" },
    key = "x",
    value = obj[key];

class A {
    foo() {
        // This is a user-defined method.
        this.eval("var a = 0");
    }

    eval() {
    }
}

Options

This rule has an option to allow indirect calls to eval. Indirect calls to eval are less dangerous than direct calls to eval because they cannot dynamically change the scope. Because of this, they also will not negatively impact performance to the degree of direct eval.

{
    "no-eval": ["error", {"allowIndirect": true}] // default is false
}

Example of incorrect code for this rule with the {"allowIndirect": true} option:

/*eslint no-eval: "error"*/

var obj = { x: "foo" },
    key = "x",
    value = eval("obj." + key);

Examples of correct code for this rule with the {"allowIndirect": true} option:

/*eslint no-eval: "error"*/

(0, eval)("var a = 0");

var foo = eval;
foo("var a = 0");

this.eval("var a = 0");
/*eslint no-eval: "error"*/
/*eslint-env browser*/

window.eval("var a = 0");
/*eslint no-eval: "error"*/
/*eslint-env node*/

global.eval("var a = 0");

Known Limitations

Further Reading

Related Rules

Version

This rule was introduced in ESLint 0.0.2.

Resources