functionlongestSubString(a,b){vararr=[];for(vari=0;i<a.length;i++){arr[i]=[];for(varj=0;j<b.length;j++){arr[i][j]=0;}}varmax=0;varindex=0;for(vari=0;i<a.length;i++){for(varj=0;j<b.length;j++){//for boundary elementif(i===0||j===0){if(a[i]===b[j]){arr[i][j]=1;max=1;}else{arr[i][j]=0;}}else{if(a[i]===b[j]){arr[i][j]=arr[i-1][j-1]+1;}else{arr[i][j]=0;}}if(max<arr[i][j]){max=arr[i][j];index=i;}}}varstr="";if(max==0){return"";}else{for(vari=index+1-max;i<=index;++i){str+=a[i];}returnstr;}}