JS遞歸實現斐波那契數列

const cache = []    
    function fi(n) {      
        if (cache[n] !== undefined) {        
            return cache[n]     
         }      
        if (n == 1 || n == 2) {          
            cache[n] = 1        
            return 1      
         }      
        cache.push(fi(n-2) + fi(n-1))      
       return cache[n]    
    }    
    console.log(fi(5)) // 5
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