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let cacheMap = new Map();let fib = n => { //1.
if ( cacheMap.has( n ) ) {
return cacheMap.get( n );
} //2.
let result = n <= 1 ? n : fib( n - 1 ) + fib( n - 2 ); //3.
cacheMap.set( n, result );return result;
}fib( 15 );