restrict-plus-operands
Require both operands of addition to be the same type and be
bigint,number, orstring.
Extending "plugin:@typescript-eslint/recommended-type-checked" in an ESLint configuration enables this rule.
This rule requires type information to run.
TypeScript allows + adding together two values of any type(s).
However, adding values that are not the same type and/or are not the same primitive type is often a sign of programmer error.
This rule reports when a + operation combines two values of different types, or a type that is not bigint, number, or string.
module.exports = {
"rules": {
"@typescript-eslint/restrict-plus-operands": "error"
}
};
Examples
- ❌ Incorrect
- ✅ Correct
var foo = '5.5' + 5;
var foo = 1n + 1;
var foo = parseInt('5.5', 10) + 10;
var foo = 1n + 1n;
Options
This rule accepts the following options
type Options = [
{
/** Whether to allow `any` typed values. */
allowAny?: boolean;
/** Whether to check compound assignments such as `+=`. */
checkCompoundAssignments?: boolean;
},
];
const defaultOptions: Options = [
{ checkCompoundAssignments: false, allowAny: false },
];
checkCompoundAssignments
Examples of code for this rule with { checkCompoundAssignments: true }:
- ❌ Incorrect
- ✅ Correct
/*eslint @typescript-eslint/restrict-plus-operands: ["error", { "checkCompoundAssignments": true }]*/
let foo: string | undefined;
foo += 'some data';
let bar: string = '';
bar += 0;
/*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
- ✅ Correct
var fn = (a: any, b: boolean) => a + b;
var fn = (a: any, b: []) => a + b;
var fn = (a: any, b: {}) => a + b;
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;
When Not To Use It
If you don't mind "[object Object]" in your strings, then you will not need this rule.