This is why I hate Javascript

this-is-why-i-hate-javascript.js

/**
 * @param {number[]} nums
 * @return {number}
 */
var removeDuplicates = function(nums) {
    if(nums.length===1) return 1;
    var i=1;
    var length = nums.length;
    var current = nums[0];
    var toDelete = [];
    while(i<length){
        if(nums[i]==current){
            toDelete.push(i);
        }
        else{
            current = nums[i];
        }
        i++;
    }
    
    while(toDelete.length) {
        nums.splice(toDelete.pop(), 1);
    }   
    return nums.length;
};

Immutability is your friend.

function removeDuplicates(nums) {
  const num_set = new Set(nums);
  nums = [...num_set.values()];
  return nums;
}