tests/cases/compiler/numericIndexExpressions.ts(10,1): error TS2322: Type 'number' is not assignable to type 'string'. tests/cases/compiler/numericIndexExpressions.ts(11,1): error TS2322: Type 'number' is not assignable to type 'string'. tests/cases/compiler/numericIndexExpressions.ts(14,1): error TS2322: Type 'number' is not assignable to type 'string'. tests/cases/compiler/numericIndexExpressions.ts(15,1): error TS2322: Type 'number' is not assignable to type 'string'. ==== tests/cases/compiler/numericIndexExpressions.ts (4 errors) ==== interface Numbers1 { 1: string; } interface Strings1 { '1': string; } var x: Numbers1; x[1] = 4; // error ~~~~ !!! error TS2322: Type 'number' is not assignable to type 'string'. x['1'] = 4; // error ~~~~~~ !!! error TS2322: Type 'number' is not assignable to type 'string'. var y: Strings1; y['1'] = 4; // should be error ~~~~~~ !!! error TS2322: Type 'number' is not assignable to type 'string'. y[1] = 4; // should be error ~~~~ !!! error TS2322: Type 'number' is not assignable to type 'string'.