Getter, Setter And Validator Functions

Attribute lets you configure getter and setter functions for each attribute. These functions are invoked when the user calls Attribute's get and set methods, and provide a way to modify the value returned or the value stored respectively.

You can also define a validator function for each attribute, which is used to validate the final value before it gets stored.

All these functions receive the value and name of the attribute being set or retrieved, as shown in the example code below. The name is not used in this example, but is provided to support use cases where you may wish to share the same function between different attributes.

Creating The Box Class - The X, Y And XY Attributes

In this example, we'll set up a custom Box class representing a positionable element, with x, y and xy attributes.

Only the xy attribute will actually store the page co-ordinate position of the box. The x and y attributes provide the user a convenient way to set only one of the co-ordinates. However we don't want to store the actual values in the x and y attributes, to avoid having to constantly synchronize all three. The getter and setter functions provide us with an easy way to achieve this. We'll define getter and setter functions for both the x and y attributes, which simply pass through to the xy attribute to store and retrieve values:

// Setup a custom class with attribute support
function Box(cfg) {

    ...
          
    // Attribute configuration
    var attrs = {

        "parent" : {
            value: null
        },

        "x" : {
            setter: function(val, name) {
                // Pass through x value to xy
                this.set("xy", [val, this.get("y")]);
            },

            getter: function(val, name) {
                // Get x value from xy
                return this.get("xy")[0];
            }
        },

        "y" : {
            setter: function(val, name) {
                // Pass through y value to xy
                this.set("xy", [this.get("x"), val]);
            },

            getter: function() {
                // Get y value from xy
                return this.get("xy")[1];
            }
        },

        "xy" : {
            // Actual stored xy co-ordinates
            value: [0, 0],

            setter: function(val, name) {
                // Constrain XY value to the parent element.

                // Returns the constrained xy value, which will
                // be the final value stored.
                return this.constrain(val);
            },

            validator: function(val, name) {
                // Ensure we only store a valid data value
                return (Y.Lang.isArray(val) && 
                        val.length == 2 && 
                        Y.Lang.isNumber(val[0]) && Y.Lang.isNumber(val[1]));
            }
        },

    ...

    this.addAttrs(attrs, cfg);

    ...
}

The validator function for xy ensures that only valid values finally end up being stored.

The xy attribute also has a setter function configured, which makes sure that the box is always constrained to it's parent element. The constrain method which it delegates to, takes the xy value the user is trying to set and returns a constrained value if the x or y values fall outside the parent box. The value which is returned by the setter is the value which is ultimately stored for the xy attribute:

// Get min, max unconstrained values for X.
Box.prototype.getXConstraints = function() {

    var parentRegion = this.get("parent").get("region"),
        nodeRegion = this._node.get("region"),
        nodeWidth = nodeRegion.right-nodeRegion.left;

    // Ceil/Floor to account for browsers which have sub-pixel values.

    return [Math.ceil(parentRegion.left + Box.BUFFER), Math.floor(parentRegion.right - nodeWidth - Box.BUFFER)];
};

// Get min, max unconstrained values for Y.
Box.prototype.getYConstraints = function() {

    var parentRegion = this.get("parent").get("region"),
        nodeRegion = this._node.get("region"),
        nodeHeight = nodeRegion.bottom-nodeRegion.top;

    // Ceil/Floor to account for browsers which have sub-pixel values.

    return [Math.ceil(parentRegion.top + Box.BUFFER), Math.floor(parentRegion.bottom - nodeHeight - Box.BUFFER)];
};

// Constrains given x,y values
Box.prototype.constrain = function(val) {

    // If the X value places the box outside it's parent,
    // modify it's value to place the box inside it's parent.

    var xConstraints = this.getXConstraints();

    if (val[0] < xConstraints[0]) {
        val[0] = xConstraints[0];
    } else {
        if (val[0] > xConstraints[1]) {
            val[0] = xConstraints[1];
        }
    }

    // If the Y value places the box outside it's parent,
    // modify it's value to place the box inside it's parent.

    var yConstraints = this.getYConstraints();

    if (val[1] < yConstraints[0]) {
        val[1] = yConstraints[0];
    } else {
        if (val[1] > yConstraints[1]) {
            val[1] = yConstraints[1];
        }
    }

    return val;
};

The setter, getter and validator functions are invoked with the host object as the context, so that they can refer to the host object using "this", as we see in the setter function for xy.

The Color Attribute - Normalizing Stored Values Through Get

The Box class also has a color attribute which also has a getter and validator functions defined:

...
"color" : {
    value: "olive",

    getter: function(val, name) {
        if (val) {
            return Y.Color.toHex(val);
        } else {
            return null;
        }
    },

    validator: function(val, name) {
        return (Y.Color.re_RGB.test(val) || Y.Color.re_hex.test(val) 
                    || Y.Color.KEYWORDS[val]);
    }
}
...

The role of the getter handler in this case is to normalize the actual stored value of the color attribute, so that users always receive the hex value, regardless of the actual value stored, which maybe a color keyword (e.g. "red"), an rgb value (e.g.rbg(255,0,0)), or a hex value (#ff0000). The validator ensures the the stored value is one of these three formats.

Syncing Changes Using Attribute Change Events

Another interesting aspect of this example, is it's use of attribute change events to listen for changes to the attribute values. Box's _bind method configures a set of attribute change event listeners which monitor changes to the xy, color and parent attributes and update the rendered DOM for the Box in response:

// Bind listeners for attribute change events
Box.prototype._bind = function() {

    // Reflect any changes in xy, to the rendered Node
    this.after("xyChange", this._syncXY);

    // Reflect any changes in color, to the rendered Node
    // and output the color value received from get
    this.after("colorChange", this._syncColor);

    // Append the rendered node to the parent provided
    this.after("parentChange", this._syncParent);

};

Since only xy stores the final co-ordinates, we don't need to monitor the x and y attributes individually for changes.

DOM Event Listeners And Delegation

Although not an integral part of the example, it's worth highlighting the code which is used to setup the DOM event listeners for the form elements used by the example:

// Set references to form controls
var xTxt = Y.one("#x");
var yTxt = Y.one("#y");
var colorTxt = Y.one("#color");

// Use event delegation for the action button clicks, and form submissions
Y.delegate("click", function(e) {

    // Get Node target from the event object

    // We already know it's a button which has an action because
    // of our selector (button.action), so all we need to do is 
    // route it based on the id.
    var id = e.currentTarget.get("id");

    switch (id) {
        case "setXY":
            box.set("xy", [parseInt(xTxt.get("value")), parseInt(yTxt.get("value"))]);
            break;
        case "setAll":
            box.set("xy", [parseInt(xTxt.get("value")), parseInt(yTxt.get("value"))]);
            box.set("color", Y.Lang.trim(colorTxt.get("value")));
            break;
        case "getAll":
            getAll();
            break;
        default:
            break;
    }

}, "#attrs", "button.action");

Rather than attach individual listeners to each button, the above code uses YUI 3's delegate support, to listen for click from buttons, with an action class which bubble up to the attrs element.

The delegate listener uses the Event Facade which normalizes cross-browser access to DOM event properties, such as currentTarget, to route to the appropriate button handler. Note the use of selector syntax when we specify the elements for the listener (e.g. #attrs, button.actions) and the use of the Node facade when dealing with references to HTML elements (e.g. xTxt, yTxt, colorTxt).

Complete Example Source

<div id="attrs" class="attrs">
    <div class="header">Enter new values and click the "Set" buttons</div>
    <div class="body">
        <ul class="hints">
            <li>Try entering valid and invalid values for x, y; or values which attempt to position the box outside it's parent (parent box co-ordinates are displayed next to the text box).</li>
            <li>Try entering rgb, hex or keyword color values [ <code>rgb(255,0,0)</code>, <code>#ff0000</code>, <code>red</code> ].</li>
        </ul>
        <div class="fields">
            <p>
                <form action="#"  id="setX" class="action">
                    <label for="x">x:</label>
                    <input type="text" name="x" id="x" />
                    <button type="submit">Set</button>
                    <span id="xhint" class="hint"></span>
                </form>
            </p>
            <p>
                <form action="#" id="setY" class="action">
                    <label for="y">y:</label>
                    <input type="text" name="y" id="y" />
                    <button type="submit">Set</button>
                    <span id="yhint" class="hint"></span>
                </form>
            </p>
            <p>
                <form action="#" id="setColor" class="action">
                    <label for="color">color:</label>
                    <input type="text" name="color" id="color" />
                    <button type="submit">Set</button>
                </form>
            </p>
        </div>
    </div>
    <div class="footer">
        <button type="button" class="action" id="setXY">Set XY</button>
        <button type="button" class="action" id="setAll">Set All</button>
        <button type="button" class="action" id="getAll">Get All</button>
    </div>
</div>

<div id="boxParent"></div>

<script type="text/javascript">
// Get a new YUI instance 
YUI().use("node", "attribute", function(Y) {

    var boxParent = Y.one("#boxParent");

    // Setup a custom class with attribute support
    function Box(cfg) {
        this._createNode(cfg);
        
        // Attribute configuration
        var attrs = {
    
            "parent" : {
                value: null
            },

            "x" : {
                setter: function(val, name) {
                    // Pass through x value to xy
                    this.set("xy", [val, this.get("y")]);
                },
    
                getter: function(val, name) {
                    // Get x value from xy
                    return this.get("xy")[0];
                }
            },

            "y" : {
                setter: function(val, name) {
                    // Pass through y value to xy
                    this.set("xy", [this.get("x"), val]);
                },
    
                getter: function() {
                    // Get y value from xy
                    return this.get("xy")[1];
                }
            },

            "xy" : {
                // Actual stored xy co-ordinates
                value: [0, 0],
    
                setter: function(val, name) {
                    // Constrain XY value to the parent element.
    
                    // Returns the constrained xy value, which will
                    // be the final value stored.
                    return this.constrain(val);
                },
    
                validator: function(val, name) {
                    // Ensure we only store a valid data value
                    return (Y.Lang.isArray(val) && val.length == 2 && Y.Lang.isNumber(val[0]) && Y.Lang.isNumber(val[1]));
                }
            },

            "color" : {
                value: "olive",
    
                getter: function(val, name) {
                    // Always normalize the returned value to 
                    // a hex color value,  even if the stored 
                    // value is a keyword, or an rgb value.
                    if (val) {
                        return Y.Color.toHex(val);
                    } else {
                        return null;
                    }
                },
    
                validator: function(val, name) {
                    // Ensure we only store rgb, hex or keyword values.
                    return (Y.Color.re_RGB.test(val) || Y.Color.re_hex.test(val) || Y.Color.KEYWORDS[val]); 
                }
            }
        };

        this.addAttrs(attrs, cfg);

        this._sync();
        this._bind();
    }

    Box.BUFFER = 5;

    // Create the box node
    Box.prototype._createNode = function() {
        this._node = Y.Node.create('<div class="yui3-box"><p>Positioned Box</p><p class="coord"></p><p class="color">None</p></div>');
    };

    // Update rendered state to match the attribute state
    Box.prototype._sync = function() {
        this._syncParent();
        this._syncXY();
        this._syncColor();
    };

    Box.prototype._syncParent = function() {
        this.get("parent").appendChild(this._node);
    };

    Box.prototype._syncXY = function() {
        this._node.setXY(this.get("xy"));
        this._node.one("p.coord").set("innerHTML", "[" + this.get("x") + "," + this.get("y") + "]");
    };

    Box.prototype._syncColor = function() {
        this._node.setStyle("backgroundColor", this.get("color"));
        this._node.one("p.color").set("innerHTML", this.get("color"));
    };

    // Bind listeners for attribute change events
    Box.prototype._bind = function() {

        // Reflect any changes in xy, to the rendered Node
        this.after("xyChange", this._syncXY);

        // Reflect any changes in color, to the rendered Node
        // and output the color value received from get
        this.after("colorChange", this._syncColor);

        // Append the rendered node to the parent provided
        this.after("parentChange", this._syncParent);

    };

    // Get min, max unconstrained values for X.
    Box.prototype.getXConstraints = function() {

        var parentRegion = this.get("parent").get("region"),
            nodeRegion = this._node.get("region"),
            nodeWidth = nodeRegion.right-nodeRegion.left;

        // Ceil/Floor to account for browsers which have sub-pixel values.

        return [Math.ceil(parentRegion.left + Box.BUFFER), Math.floor(parentRegion.right - nodeWidth - Box.BUFFER)];
    };

    // Get min, max unconstrained values for Y.
    Box.prototype.getYConstraints = function() {

        var parentRegion = this.get("parent").get("region"),
            nodeRegion = this._node.get("region"),
            nodeHeight = nodeRegion.bottom-nodeRegion.top;

        // Ceil/Floor to account for browsers which have sub-pixel values.

        return [Math.ceil(parentRegion.top + Box.BUFFER), Math.floor(parentRegion.bottom - nodeHeight - Box.BUFFER)];
    };

    // Constrain the x,y value provided
    Box.prototype.constrain = function(val) {

        // If the X value places the box outside it's parent,
        // modify it's value to place the box inside it's parent.

        var xConstraints = this.getXConstraints();

        if (val[0] < xConstraints[0]) {
            val[0] = xConstraints[0];
        } else {
            if (val[0] > xConstraints[1]) {
                val[0] = xConstraints[1];
            }
        }

        // If the Y value places the box outside it's parent,
        // modify it's value to place the box inside it's parent.

        var yConstraints = this.getYConstraints();

        if (val[1] < yConstraints[0]) {
            val[1] = yConstraints[0];
        } else {
            if (val[1] > yConstraints[1]) {
                val[1] = yConstraints[1];
            }
        }
        return val;
    };


    Y.augment(Box, Y.Attribute);

    // ------

    // Create a new instance of Box
    var box = new Box({
        parent : boxParent 
    });

    // Set references to form controls
    var xTxt = Y.one("#x");
    var yTxt = Y.one("#y");
    var colorTxt = Y.one("#color");

    var xHint = Y.one("#xhint");
    var yHint = Y.one("#yhint");

    function getAll() {
        xTxt.set("value", box.get("x"));
        yTxt.set("value", box.get("y"));
        colorTxt.set("value", box.get("color"));
    }

    // Use event delegation for the action button clicks, and form submissions
    Y.delegate("click", function(e) {

        // Get Node target from the event object

        // We already know it's a button which has an action because
        // of our selector (button.action), so all we need to do is 
        // route it based on the id.
        var id = e.currentTarget.get("id");

        switch (id) {
            case "setXY":
                box.set("xy", [parseInt(xTxt.get("value"), 10), parseInt(yTxt.get("value"), 10)]);
                break;
            case "setAll":
                box.set("xy", [parseInt(xTxt.get("value"), 10), parseInt(yTxt.get("value"), 10)]);
                box.set("color", Y.Lang.trim(colorTxt.get("value")));
                break;
            case "getAll":
                getAll();
                break;
            default:
                break;
        }

    }, "#attrs", "button.action");

    Y.all("#attrs form.action").on("submit", function(e) {

        e.preventDefault();

        // Get Node target from the event object

        // We already know it's a button which has an action because
        // of our selector (button.action), so all we need to do is 
        // route it based on the id.
        var id = e.currentTarget.get("id");

        switch (id) {
            case "setX":
                box.set("x", parseInt(xTxt.get("value"), 10));
                break;
            case "setY":
                box.set("y", parseInt(yTxt.get("value"), 10));
                break;
            case "setColor":
                box.set("color", Y.Lang.trim(colorTxt.get("value")));
                break;
            default:
                break;
        }
    });

    // Bind listeners to provide min, max unconstrained value hints for x, y
    // (focus/blur doesn't bubble, so bind individual listeners)
    Y.on("focus", function() {
        var minmax = box.getXConstraints();
        xHint.set("innerHTML", "Valid values: " + minmax[0] + " to " + minmax[1]);
    }, xTxt);

    Y.on("focus", function() {
        var minmax = box.getYConstraints();
        yHint.set("innerHTML", "Valid values: " + minmax[0] + " to " + minmax[1]);
    }, yTxt);

    Y.on("blur", function() {
        xHint.set("innerHTML", "");
    }, xTxt);

    Y.on("blur", function() {
        yHint.set("innerHTML", "");
    }, yTxt);

    getAll();
});
</script>