[ [numer_1, denom_1] , ... [numer_n, denom_n] ]

[ [1, 2], [1, 3], [1, 4] ] // => (6,12)(4,12)(3,12)

//smallest common multiple 
function scm(array){ 
 var max = Math.max.apply(null,array); 
 signal: 
 while(true){ 
 for(var i=0;i<array.length;i++){ 
 if(max % array[i]){ 
 max++; 
 continue signal; 
 } 
 } 
 return max; 
 } 
}

function convertFrac(lst){ 
 var array = []; 
 var str = ""; 
 for(var i=0;i<lst.length;i++){ 
 array.push(lst[i][1]); 
 } 
 var result = scm(array); 
 for(var i=0;i<lst.length;i++){ 
 str += "(" + result / lst[i][1] * lst[i][0] + "," + result + ")"; 
 } 
 return str; 
}