JS.TS.RESTRICT.PLUS.OPERANDS

When adding two variables, operands must both be of type number or of type string

Rule Details

Examples of code for this rule:

Incorrect

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var foo = '5.5' + 5;
var foo = 1n + 1;

Correct

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var foo = parseInt('5.5', 10) + 10;
var foo = 1n + 1n;

Options

The rule accepts an options object with the following properties:

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type Options = {
  // if true, check compound assignments (`+=`)
  checkCompoundAssignments?: boolean;
  // if true, 'any' itself and `string`,`bigint`, `number` is allowed.
  allowAny?: boolean;
};

const defaults = {
  checkCompoundAssignments: false,
  allowAny: false,
};

`checkCompoundAssignments`

Examples of code for this rule with { checkCompoundAssignments: true }:

Incorrect

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/*eslint @typescript-eslint/restrict-plus-operands: ["error", { "checkCompoundAssignments": true }]*/

let foo: string | undefined;
foo += 'some data';

let bar: string = '';
bar += 0;

Correct

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/*eslint @typescript-eslint/restrict-plus-operands: ["error", { "checkCompoundAssignments": true }]*/

let foo: number = 0;
foo += 1;

let bar = '';
bar += 'test';

`allowAny`

Examples of code for this rule with { allowAny: true }:

Incorrect

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var fn = (a: any, b: boolean) => a + b;
var fn = (a: any, b: []) => a + b;
var fn = (a: any, b: {}) => a + b;

Correct

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var fn = (a: any, b: any) => a + b;
var fn = (a: any, b: string) => a + b;
var fn = (a: any, b: bigint) => a + b;
var fn = (a: any, b: number) => a + b;

How to Use

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{
  "@typescript-eslint/restrict-plus-operands": "error"
}