Check for undefined property in object in EJS in Node.JS

Question

I have an object, called user, which may or may not have subproperties defined. For example, sometimes there is no "pages" object, sometimes you can go user.pages.someothervariable.

I can see in EJS how to check that user exists, but how can I check that user.pages.someothervariable exists without getting a "cannot access property of undefined" error.

I've tried this and typeof, but cannot get it to work.

<% if(locals.user.pages.pageVisits){ %>foo defined<% }else{ %>foo undefined<% } %>

I get this error:

Cannot read property 'pageVisits' of undefined

score 1 · Accepted Answer · 2018-05-19 21:51:16Z

1

You can use short-circuiting && --

if(locals.user.pages && locals.user.pages.pageVisits) { /* do sth */ }

If user.pages is falsy, the evaluation won't proceed.

If the chain gets too long, you can try to encapsulate it into a function, like --

function getPage(user) {
    return (user && user.pages && user.pages.accountPage)
        || "0"; // a fallback if the left side is falsy
}

edited May 19, 2018 at 21:51

answered May 19, 2018 at 21:25

user9539019

Sign up to request clarification or add additional context in comments.

1 Comment

user1149620 Over a year ago

Thanks, is there a more elegant way than this at all: <%= (user && user.pages && user.pages.pageVisits && user.pages.pageVisits.accountPage) ? user.pages.pageVisits.accountPage : '0' %>

Michael Karpinski · Accepted Answer · 2018-05-19 21:56:21Z

0

You can check if your user has a pages field by running if(local.user.pages). This is because almost any value can be evaluated in if statements in JS. If user.pages is null, then the if statement will return false. If user.pages exists it will return true.

You could do a try-catch to avoid messiness:

var obj = {
  test: "hello"
}

try {
  console.log(obj.fakeKey.otherFakeKey)
}
catch(ex) {
  console.log("Caught")
}

edited May 19, 2018 at 21:56

answered May 19, 2018 at 21:20

Michael Karpinski

3632 silver badges11 bronze badges

7 Comments

user1149620 Over a year ago

Thanks, this works, but I guess I have to nest a lot to get this to work and the code ends up very messy. Do you know if there is a more elegant solution?

Michael Karpinski Over a year ago

Using a try-catch could clean it up. I edited my post

user9539019 Over a year ago

"Using a try-catch could clean it up" -- you're kidding, aren't you.

Michael Karpinski Over a year ago

What's wrong with a try-catch? It might not be the #1 cleanest way to go about it, but it's better than convoluted boolean logic in certain cases

user9539019 Over a year ago

Well, leaving aside performance penalties and the fact that there is nothing exceptional here (why try and throw?), how would you recover if all you wanted to do is to simply set a variable

<%= (user && user.pages && user.pages.pageVisits && user.pages.pageVisits.accountPage) ? user.pages.pageVisits.accountPage : '0' %>

. OP doesn't want to log anything, he wants the value to be 0 if there is no such prop.

|

Collectives™ on Stack Overflow

Check for undefined property in object in EJS in Node.JS

2 Answers 2

1 Comment

7 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

7 Comments

Your Answer

Sign up or log in

Post as a guest

Related