Merge Intervals 

/**
 * @param {number[][]} intervals
 * @return {number[][]}
 */
var merge = function(intervals) {
    let uniqueIntervals=[];
    let curr=[intervals[0]];
    
    intervals= intervals.sort((a,b)=>(a[0]-b[0]))
    
    for(let x of intervals){
        //console.log("int ",uniqueIntervals, " ",curr," ",x)
        if(curr[1]>=x[0]){
            //console.log("if")
            curr[1]=Math.max(curr[1] , x[1])
            //curr[1] = 'sm'
        }
        
        else{
          console.log(x)
            uniqueIntervals.push(x);
            curr=x;
             
        }
       
    }
    
    return uniqueIntervals
};

console.log(merge([[1,3],[2,6],[8,10],[15,18]]))