function arrayPreviousLess(nums) {
    // Null && undefined check
    if (nums === null || nums === undefined) {
        alert("Nothing comes from nothing")
        return null
    }
    
    // Convert string to array
    if (typeof(nums) === "string") nums = nums.split("")
    
    // Check that only numbers are present
    typeCheckedNums = nums.map(num => {
        if (typeof(num) !== "number") num = Number(num)
        if (isNaN(num)) {
            return null
        }
        return num
    })
    
    if (typeCheckedNums.includes(null)) {
        alert("Only items that are or can be converted to type number are allowed")
        return null
    }
    
    // The real stuff ...
    let items = typeCheckedNums.length
    let backerds = typeCheckedNums.reverse()
    let output = []
    for (let i=0; i<items; i++) {
        let sifted = backerds.filter(n => n < backerds[0])
        let insert = (sifted.length === 0) ? -1 : sifted[0]
        output.push(insert)
        backerds.shift()
    }
    output.reverse()
    return output
}



/**
* Test Suite 
*/
describe('arrayPreviousLess()', () => {
    it('shift previous postions from the left to a smaller value or store -1', () => {
        // arrange
        const nums = [3, 5, 2, 4, 5];
        
        // act
        const result = arrayPreviousLess(nums);

        // log
        console.log("result: ", result);
        
        // assert
        expect(result).toEqual([-1, 3, -1, 2, 4]);
    });
    
    it('alerts if null or undefined values are passed and returns null', () => {
        // arrange
        const nums = null;
        
        // act
        const result = arrayPreviousLess(nums);

        // log
        console.log("result: ", result);
        
        // assert
        expect(result).toEqual(null);
    });
    
    it('converts strings of numbers to an array', () => {
        // arrange
        const str = "35245";
        
        // act
        const result = arrayPreviousLess(str);

        // log
        console.log("result: ", result);
        
        // assert
        expect(result).toEqual([-1, 3, -1, 2, 4]);
    });
    
    it('alerts and returns null if input cannot be converted to an array of numbers', () => {
        // arrange
        const str = "3e24ff";
        
        // act
        const result = arrayPreviousLess(str);

        // log
        console.log("result: ", result);
        
        // assert
        expect(result).toEqual(null);
    });
});