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

This rule has an object option:

• "checkCompoundAssignments": false: (default) does not check compound assignments (+=)
• "checkCompoundAssignments": true

checkCompoundAssignments

Examples of code for the { "checkCompoundAssignments": true } option:

❌ 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';

How to use

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

Compatibility

• TSLint: restrict-plus-operands

Attributes

• ✅ Recommended
• 🔧 Fixable
• 💭 Requires type information