Javascript object property detection

Question

What is the least amount of code needed to do the following:

If an object exists and it has a required property and the property is not an empty string then set a variable to the value of the property else set the variable to a default string.

Assuming that the object variable can only be undefined or a valid object, it can never be a function, null, string or anything else. Also if the object has the required property it is a string and never anything else.

A solution to this maybe:

// obj is the object we are testing, prop is the name of the property, def is the default string

var result = def;
if (obj && obj[prop] && obj[prop].length) {
    result = obj[prop];
}

Whether this is completely correct I am unsure.

But is there a shorter way?

Thanks,

AJ

This is how I would do it. It's readable and does what you intend. — kinakuta
– kinakuta, Commented Oct 2, 2014 at 15:27
Since this question about looking to optimize working code, i've flagged it for migration to Code Review. — Scimonster
– Scimonster, Commented Oct 2, 2014 at 15:28

Barmar · Accepted Answer · 2014-10-02 15:30:29Z

2

If you want to shorten it, you can write:

result = (obj && obj[prop]) || def;

An empty string is falsy, so you don't need to check the length explicitly.

result = <val> || <default>;

is a common idiom for setting a variable to a value, with a default if the value is null.

answered Oct 2, 2014 at 15:30

Barmar

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1 Comment

AJ. Over a year ago

I didn't know that an empty string was falsy, that is actually very helpful. Thanks

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