Function isInteger(x) that determines if x is an integer.

integer.js

// isInteger(3);   // Outputs true 
// isInteger("5");   // Outputs false
// isInteger("car");   // Outputs false 

function isInteger(x) { 
    // ^ stands for XOR so every integer with (4^0) will give integer itself. Every string will give 0
    return (x^0) === x; 
} 

// Another solution

function isInteger(x){
    return Math.round(x) == x;
}