Knockout Helpers

kov.js

/**
 * Lookup the observable object or value of a field safely no matter if it is static or observable or even exists
 * @syntax kov([scope,]period_delimited_lookup_string[,ifmissing])
 * @returns value or ifmissing
 * @author Eric Freed
 */
function kov(a, b, c, orig_f, orig_scope) {
	try {
		var ifmissing, f, _scope = "init";
		if (typeof a == "string") {
			_scope = (ko.contextFor(document.body)||{}).$data;
			f = a+"";
			ifmissing = b;
		} else {
			_scope = a;
			f = b+"";
			ifmissing = c;
		}
		// Grab first element in a dot-notation field
		var path = f.split(".");
		f = path.shift();

		if (typeof _scope === undefined)
			throw "scope is empty"; 
		if ( !(_scope.hasOwnProperty(f) || f in _scope) )
			throw "property is undefined"; 
		if (typeof _scope === "string" && !isNaN(f))
			throw "you didn't mean to ask for a character in a string, right?"; 
		var field_found = _scope[f];
		if (path.length) {
			// Drill in to next level
			if (typeof field_found == "function")
				field_found = field_found();
			return kov(field_found, path.join("."), ifmissing, orig_f || (f+"."+(path.join('.'))), orig_scope || _scope);
		} else {
			if (field_found === undefined)
				return ifmissing;
			return field_found;
		}
	} catch(e) {
		if (f === undefined)
			console.log("error loading kov", a, b, c);
		if (ifmissing === undefined) {
			if (orig_f) {
				console.log("error in kov("+f+")", e, _scope, "_orig_", orig_f, orig_scope);
			} else {
				console.log("error in kov("+f+")", e, _scope);
			}
			if (typeof window.Error == "function") {
				var err = new Error();
				console.log('stack from above error: ', err.stack);
			}
			if (window.Rollbar) {
				 Rollbar.warning("error in kov("+f+")", {
					 js_error: e,
					 scope: _scope,
					 orig_search: orig_f,
					 orig_scope: orig_scope
				 });
			}
		}
		return ifmissing;
	}
}
// Safe shorthand for kov(...)()
function v(a, b, c) {
	var v = this.kov(a, b, c);
	if (typeof v === "function")
		return v();
	return v;
}

// Numeric extender from KO's Documentation
ko.extenders.numeric = function(target, precision) {
    //create a writable computed observable to intercept writes to our observable
    var result = ko.pureComputed({
        read: target,  //always return the original observables value
        write: function(newValue) {
            var current = target(),
                roundingMultiplier = Math.pow(10, precision),
                newValueAsNum = isNaN(newValue) ? 0 : parseFloat(+newValue),
                valueToWrite = Math.round(newValueAsNum * roundingMultiplier) / roundingMultiplier;
 
            //only write if it changed
            if (valueToWrite !== current) {
                target(valueToWrite);
            } else {
                //if the rounded value is the same, but a different value was written, force a notification for the current field
                if (newValue !== current) {
                    target.notifySubscribers(valueToWrite);
                }
            }
        }
    }).extend({ notify: 'always' });
 
    //initialize with current value to make sure it is rounded appropriately
    result(target());
 
    //return the new computed observable
    return result;
};