Sodoku Solver - created for websudoku.com but can altered to work for any sodoku website.

main.js

(function(){
    /**
    * A single sodoku cell
    */
    var cell = function(col, row) {
        this.col = col;
        this.row = row;
        this.block = (Math.floor(col / 3) * 10) + Math.floor(row / 3);
        this.id = "f" + col + "" + row;
        this.value = document.getElementById(this.id).value;
        this.value = this.value.indexOf(',') !== -1 ? "" : this.value;
        this.numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9];
    };

    cells = [];

    /**
    * Sets the cells value
    */
    cell.prototype.setValue = function(val) {
        var dom = document.getElementById(this.id);
        var valChange = dom.value !== val;
        dom.value = val;
        dom.onkeyup();
        return valChange;
    };
    
    /**
    * Returns all cells on this row
    */
    cell.prototype.cellRow = function() {
        var thatRow = this.row;
        return cells.filter(function(ob) {
            return ob.row === thatRow;
        });
    };

    /**
    * Returns all cells on this column
    */
    cell.prototype.cellCol = function() {
        var thatCol = this.col;
        return cells.filter(function(ob) {
            return ob.col === thatCol; 
        });
    };

    /**
    * Returns all cells in this block
    */
    cell.prototype.cellBlock = function() {
        var thatBlock = this.block;
        return cells.filter(function(ob) {
            return ob.block === thatBlock;
        });
    };

    /**
    * Guesses the cells value based on possible numbers. 
    * If there is only one possible number, that must be the answer
    */
    cell.prototype.cellGuess = function() {
        var myCells = [...this.cellRow(), ...this.cellCol(), ...this.cellBlock()];

        for(var i = myCells.length - 1; i >= 0; i--)
            this.numbers = checkCell(myCells[i], this.numbers);

        if(this.numbers.length === 1) {
            this.setValue(this.numbers.toString());
            this.value = this.numbers.toString();
            changed = true;
        }
        else if(this.setValue(this.numbers.join(',')))
                changed = true;
    };
    
    /**
    * Guesses the cells value based on possible numbers. 
    * If this cell is the only one that can hold this number, that number must belong to this cell
    */
    cell.prototype.numberGuess = function () {
        var myCells = [this.cellRow(), this.cellCol(), this.cellBlock()];
        
        for(var k = myCells.length - 1; k >= 0; k--) {
            for(var j = this.numbers.length - 1; j >= 0; j--) {
                var found = false;
                
                for(var i = myCells[k].length - 1; i >= 0; i--) {
                    if(myCells[k][i].id !== this.id && checkNumber(myCells[k][i], this.numbers[j])) {
                        found = true;
                        break;   
                    }
                }

                if(!found){
                    this.setValue(this.numbers[j]);
                    this.value = this.numbers[j];
                    changed = true;
                    return;
                }
            }
        }
    };

    /**
    * Guesses the cells value based on possible numbers. 
    * If there is only one possible number, that must be the answer
    */
    var checkCell = function(c, numbers) {
        if(c.value) 
            return numbers.filter(function(num) {
                return num !== parseInt(c.value);
            });

        return numbers;
    };
    
    /**
    * Guesses the cells value based on possible numbers. 
    * If this cell is the only one that can hold this number, that number must belong to this cell
    */
    var checkNumber = function(c, number) {
        if(c.value)
            return c.value == number;
        
        return c.numbers.indexOf(number) !== -1;
    };

    /**
    * Gets all the cells in an array
    */
    for(var i = 0; i <= 8; i++)
        for(var j = 0; j <= 8; j++)
            cells.push(new cell(i, j));

    var changed = false;
    /**
    * Attempts to solve the puzzle
    */
    var solve = function () {
        cellGuess();
        var count = 0;

        while(changed && count < 100) {
            count++;
            changed = false;
            cellGuess();
            numberGuess();
        }
        if(changed) {
            console.log("ERROR 1");       
            return;
        }
        
        for(var i = cells.length - 1; i >= 0; i--) {
            if(!cells[i].value) {
                console.log("could not solve");
                return;
            }
        }
        
        console.log('solved in ' + count + ' iterations');
    };

    /**
    * Guesses the cells value based on possible numbers. 
    * If there is only one possible number, that must be the answer
    */
    var cellGuess = function () {
        for(var i = cells.length - 1; i >= 0; i--) {
            if(cells[i].value) 
                continue;

            cells[i].cellGuess();
        }
    };
    
    /**
    * Guesses the cells value based on possible numbers. 
    * If this cell is the only one that can hold this number, that number must belong to this cell
    */
    var numberGuess = function () {
        for(var i = cells.length - 1; i >= 0; i--) {
            if(cells[i].value)
                continue;
            
            cells[i].numberGuess();
        }
    };
   
    solve();
})();