Select grand child in array knockout

Question

I'm trying to select a grand child from an array in an array.

If it was C# I would have wrote something like below

SubSteps.Select(item => item.First(subitem => subitem == 1)).First();

I have code that works, but I'm not sure it is the best way to do it:

ko.utils.arrayFirst(ko.utils.arrayFirst(self.SubSteps(),
 function (item) {
 return ko.utils.arrayFirst(item.SubSteps(),
 function (subItem) { return subItem.InternalName == localStorage.getItem('lastWizardPage'); });
 }).SubSteps(), function (item) {
 return item.InternalName == localStorage.getItem('lastWizardPage');
 })

Is there a method I can use that I've never heard of perhaps?

Answer 1

Interesting question.

First off, your indentation is terrible, your code is far more readable like this:

ko.utils.arrayFirst(ko.utils.arrayFirst(self.SubSteps(),
 function(item) {
 return ko.utils.arrayFirst(item.SubSteps(),
 function(subItem) {
 return subItem.InternalName == localStorage.getItem('lastWizardPage');
 });
 }).SubSteps(), function(item) {
 return item.InternalName == localStorage.getItem('lastWizardPage');
})

Second, you are retrieving your subitem twice, because you loose track of it, simply use a 'local global' and assign your subitem to it.

var needle, found;
ko.utils.arrayFirst(self.SubSteps(),
 function(item) {
 return ko.utils.arrayFirst(item.SubSteps(),
 function(subItem) {
 found = subItem.InternalName == localStorage.getItem('lastWizardPage');
 if(found) {
 needle = subItem;
 }
 return found;
 });
 });

or, if you dont mind some sorcery (don't do this at work!)

var needle, found;
ko.utils.arrayFirst(self.SubSteps(),
 function(item) {
 return ko.utils.arrayFirst(item.SubSteps(),
 function(subItem) {
 found = subItem.InternalName == localStorage.getItem('lastWizardPage');
 return found && (needle = subItem), found;
 });
 });

Furthemore, you should consider caching localStorage.getItem('lastWizardPage') and you should consider implementing old skool loops so that you can exit immediately.

• Pochen: Thank you. The intendention is better in my IDE, but broke here. About the rest of the code worked really good. Thank you!

Answer 2

It looks like you could use recursion to simplify your code, unless the grandchildren have children that you want to avoid, this should work.

function findLastWizard(arr) {
 var subArrayOrItem = ko.utils.arrayFirst(arr, function(item) {
 return item.InternalName == localStorage.getItem('lastWizardPage');
 });
 if(subArrayOrItem.SubSteps) {
 return findLastWizard(subArrayOrItem.SubSteps());
 }
 return subArrayOrItem;
}
findLastWizard(self.SubSteps())