Avoid duplicate keys in object literals

Documentos > Code Analysis > Static Analysis Rules > Avoid duplicate keys in object literals

This page is not yet available in Spanish. We are working on its translation.
If you have any questions or feedback about our current translation project, feel free to reach out to us!

Metadata

ID: typescript-best-practices/no-dupe-keys

Language: TypeScript

Severity: Error

Category: Error Prone

Description

Object literals should not have duplicate keys. If you define an object with duplicate keys, the last one will overwrite any preceding ones.

Non-Compliant Code Examples

var x = { a: b, ['a']: b };
var x = { y: 1, y: 2 };
var x = { '': 1, '': 2 };
var x = { '': 1, [``]: 2 };
var foo = { 0x1: 1, 1: 2};
// should be captured by no-octal
// var x = { 012: 1, 10: 2 };
var x = { 0b1: 1, 1: 2 };
var x = { 0o1: 1, 1: 2 };
var x = { 1n: 1, 1: 2 };
var x = { 1_0: 1, 10: 2 };
var x = { "z": 1, z: 2 };
var foo = {
  bar: 1,
  bar: 1,
  bar() {}
}
var x = { a: 1, get ['a']() {} };
var x = { a: 1, set a(value) {} };
var x = { a: 1, b: { a: 2 }, get b() {} };
var x = ({ '/(?<zero>0)/': 1, [/(?<zero>0)/]: 2 })

// while we can't evaluate the value of the template string we will assume that
// two keys with the exact same template string will evaluate to the same key
const obj = {
    props: {
        [`${classes.foo} ${classes.bar}`]: (): boolean => {
            return null;
        },
        [`${classes.foo} ${classes.bar}`]: (): boolean => {
            return null;
        },
    }
}

Compliant Code Examples

var foo = { __proto__: 1, two: 2};
var x = { foo: 1, bar: 2 };
var x = { '': 1, bar: 2 };
var x = { '': 1, ' ': 2 };
var x = { '': 1, [null]: 2 };
var x = { '': 1, [a]: 2 };
var x = { [a]: 1, [a]: 2 };

var x = { a: b, [a]: b };
var x = { a: b, ...c }

var x = { a: 1, b: { a: 2 } };
var x = ({ null: 1, [/(?<zero>0)/]: 2 })
var {a, a} = obj
// should be captured by no-octal
// var x = { 012: 1, 12: 2 };
var x = { 1_0: 1, 1: 2 };

// template literals should be valid as long as they are not exactly the same
const obj = {
    props: {
        [`${classes.foo} ${classes.bar}`]: (): boolean => {
            return null;
        },
        [`${classes.baz} ${classes.bla}`]: (): boolean => {
            return null;
        },
    }
}