When adding two variables, operands must both be of type number or of type string (restrict-plus-operands)

Rule Details

Examples of code for this rule:

❌ Incorrect

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

✅ Correct

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

Options

The rule accepts an options object with the following properties:

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

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

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

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

✅ Correct

/*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

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

✅ Correct

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

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

Related To

• TSLint: restrict-plus-operands

Attributes

• ✅ Recommended
• 🔧 Fixable
• 💭 Requires type information