accessor-pairs

Enforce getter and setter pairs in objects and classes

It’s a common mistake in JavaScript to create an object with just a setter for a property but never have a corresponding getter defined for it. Without a getter, you cannot read the property, so it ends up not being used.

Here are some examples:

// Bad
var o = {
    set a(value) {
        this.val = value;
    }
};


// Good
var o = {
    set a(value) {
        this.val = value;
    },
    get a() {
        return this.val;
    }
};

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This rule warns if setters are defined without getters. Using an option getWithoutSet, it will warn if you have a getter without a setter also.

Rule Details

This rule enforces a style where it requires to have a getter for every property which has a setter defined.

By activating the option getWithoutSet it enforces the presence of a setter for every property which has a getter defined.

This rule always checks object literals and property descriptors. By default, it also checks class declarations and class expressions.

Options

• setWithoutGet set to true will warn for setters without getters (Default true).
• getWithoutSet set to true will warn for getters without setters (Default false).
• enforceForClassMembers set to true additionally applies this rule to class getters/setters (Default true). Set enforceForClassMembers to false if you want this rule to ignore class declarations and class expressions.

setWithoutGet

Examples of incorrect code for the default { "setWithoutGet": true } option:

/*eslint accessor-pairs: "error"*/

var o = {
    set a(value) {
        this.val = value;
    }
};


var o = {d: 1};
Object.defineProperty(o, 'c', {
    set: function(value) {
        this.val = value;
    }
});
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Examples of correct code for the default { "setWithoutGet": true } option:

/*eslint accessor-pairs: "error"*/

var o = {
    set a(value) {
        this.val = value;
    },
    get a() {
        return this.val;
    }
};

var o = {d: 1};
Object.defineProperty(o, 'c', {
    set: function(value) {
        this.val = value;
    },
    get: function() {
        return this.val;
    }
});

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getWithoutSet

Examples of incorrect code for the { "getWithoutSet": true } option:

/*eslint accessor-pairs: ["error", { "getWithoutSet": true }]*/

var o = {
    set a(value) {
        this.val = value;
    }
};

var o = {
    get a() {
        return this.val;
    }
};

var o = {d: 1};
Object.defineProperty(o, 'c', {
    set: function(value) {
        this.val = value;
    }
});

var o = {d: 1};
Object.defineProperty(o, 'c', {
    get: function() {
        return this.val;
    }
});
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Examples of correct code for the { "getWithoutSet": true } option:

/*eslint accessor-pairs: ["error", { "getWithoutSet": true }]*/
var o = {
    set a(value) {
        this.val = value;
    },
    get a() {
        return this.val;
    }
};

var o = {d: 1};
Object.defineProperty(o, 'c', {
    set: function(value) {
        this.val = value;
    },
    get: function() {
        return this.val;
    }
});

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enforceForClassMembers

When enforceForClassMembers is set to true (default):

• "getWithoutSet": true will also warn for getters without setters in classes.
• "setWithoutGet": true will also warn for setters without getters in classes.

Examples of incorrect code for { "getWithoutSet": true, "enforceForClassMembers": true }:

/*eslint accessor-pairs: ["error", { "getWithoutSet": true, "enforceForClassMembers": true }]*/

class Foo {
    get a() {
        return this.val;
    }
}

class Bar {
    static get a() {
        return this.val;
    }
}

const Baz = class {
    get a() {
        return this.val;
    }
    static set a(value) {
        this.val = value;
    }
}
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Examples of incorrect code for { "setWithoutGet": true, "enforceForClassMembers": true }:

/*eslint accessor-pairs: ["error", { "setWithoutGet": true, "enforceForClassMembers": true }]*/

class Foo {
    set a(value) {
        this.val = value;
    }
}

const Bar = class {
    static set a(value) {
        this.val = value;
    }
}
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When enforceForClassMembers is set to false, this rule ignores classes.

Examples of correct code for { "getWithoutSet": true, "setWithoutGet": true, "enforceForClassMembers": false }:

/*eslint accessor-pairs: ["error", {
    "getWithoutSet": true, "setWithoutGet": true, "enforceForClassMembers": false
}]*/

class Foo {
    get a() {
        return this.val;
    }
}

class Bar {
    static set a(value) {
        this.val = value;
    }
}

const Baz = class {
    static get a() {
        return this.val;
    }
}

const Quux = class {
    set a(value) {
        this.val = value;
    }
}
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Known Limitations

Due to the limits of static analysis, this rule does not account for possible side effects and in certain cases might not report a missing pair for a getter/setter that has a computed key, like in the following example:

/*eslint accessor-pairs: "error"*/

var a = 1;

// no warnings
var o = {
    get [a++]() {
        return this.val;
    },
    set [a++](value) {
        this.val = value;
    }
};
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Also, this rule does not disallow duplicate keys in object literals and class definitions, and in certain cases with duplicate keys might not report a missing pair for a getter/setter, like in the following example:

/*eslint accessor-pairs: "error"*/

// no warnings
var o = {
    get a() {
        return this.val;
    },
    a: 1,
    set a(value) {
        this.val = value;
    }
};
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The code above creates an object with just a setter for the property "a".

See no-dupe-keys if you also want to disallow duplicate keys in object literals.

See no-dupe-class-members if you also want to disallow duplicate names in class definitions.

When Not To Use It

You can turn this rule off if you are not concerned with the simultaneous presence of setters and getters on objects.

Related Rules

• no-dupe-keys
• no-dupe-class-members

Version

This rule was introduced in ESLint v0.22.0.

Further Reading

setter - JavaScript | MDN
developer.mozilla.org

getter - JavaScript | MDN
developer.mozilla.org

Working with objects - JavaScript | MDN
developer.mozilla.org

Resources

• Rule source
• Tests source