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

Examples of correct code:

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

Examples of incorrect code:

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

Options

This rule has an object option:

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

checkCompoundAssignments

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

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

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

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

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

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

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

let bar = '';
bar += 'test';
{
  "@typescript-eslint/restrict-plus-operands": "error"
}

Compatibility

Attributes

  • ✅ Recommended
  • 🔧 Fixable
  • 💭 Requires type information