Tests if given object is an arrray. forEach runs a given function on each element in the array. It doesn't return anything. map runs a function on each element and which returns a value for each element and returns a new array with these values. filter runs a boolean function against every element and returns an array of the values that resulted in a true value. reduce runs a function on each element and returns a single value. array.every checks every element in an array and returns true if every element meets the given condition. array.some returns a true value if at least 1 element meets the given condition. Returns the index of the 1st occurence of the given value in an array and -1 if not found. Returns the index of the last occurence of the given value in an array and -1 if not found.