JSFiddle - React, Tailwind, and code Playground

JavaScript

var array=[1,2,3,4,5,6,7,8,9,0,1,2,1];
function toUnique(a,b,c){//array,placeholder,placeholder
 b=a.length;
 while(c=--b)while(c--)a[b]!==a[c]||a.splice(c,1);
 return a;
}
console.log(array);
console.log(toUnique(array));