mapGetOrInsert.ts(11,13): error TS2339: Property 'getOrInsert' does not exist on type 'ReadonlyMap<string, number>'.


==== mapGetOrInsert.ts (1 errors) ====
    const map = new Map<string, number>();
    const inserted: number = map.getOrInsert("a", 1);
    const computed: number = map.getOrInsertComputed("b", key => key.length);
    
    const weakMap = new WeakMap<object, number>();
    const key = {};
    const weakInserted: number = weakMap.getOrInsert(key, 1);
    const weakComputed: number = weakMap.getOrInsertComputed(key, value => value === key ? 1 : 0);
    
    declare const readonlyMap: ReadonlyMap<string, number>;
    readonlyMap.getOrInsert("a", 1);
                ~~~~~~~~~~~
!!! error TS2339: Property 'getOrInsert' does not exist on type 'ReadonlyMap<string, number>'.
    