JSFiddle - React, Tailwind, and code Playground

JavaScript

var array1 = [100,200,300,400];
var array2 = [100,200];
function array_diff(arr1,arr2)
{
    var x = Math.max(arr1.length,arr2.length);
    for(var i = 0; i < x; i++)
    {
        if(typeof arr1[i] !== 'undefined' && arr2.indexOf(arr1[i]) != -1)
            arr1.splice(i,1);
        if(typeof arr2[i] !== 'undefined' && arr1.indexOf(arr2[i]) != -1)
            arr1.splice(arr1.indexOf(arr2[i]),1);
    }
    return arr1;
}
console.log(array_diff(array1,array2));