A comprehensive method in JavaScript to determine if a variable is defined

Question

A comprehensive method in JavaScript to determine if a variable is defined

There was a moment when I recall stumbling upon a code snippet that utilized a javascript library, possibly lodash, to perform a comprehensive check for the existence of a certain element.

For instance:

someLib.isDefined(anObject.aNestedObject.anotherNestedObject);

This function would return true if anotherNestedObject exists, but it would return false without causing an error if anObject or aNestedObject were not defined.

Is this just a figment of my imagination, or does a popular function capable of this task actually exist?

javascript typescript

Answer 1

Answer №1

In my previous response, I mentioned that it may not be feasible to achieve what you are looking for.

The code snippet

anObject.aNestedObject.anotherNestedObject

gets executed prior to calling the someLib.isDefined function. This means that if either anObject or aNestedObject do not exist, an exception will be thrown before the function can be utilized.

One workaround could be passing the expression as a string, like this:

someLib.isDefined("anObject.aNestedObject.anotherNestedObject")

Alternatively, you can perform a check like this:

if (anObject && anObject.aNestedObject && anObject.aNestedObject.anotherNestedObject) {
    // do something
}

Another option is to create your own function, which is quite straightforward:

function exists(obj: any, keys: string | string[]) {
    if (typeof keys === "string") {
        keys = keys.split(".");
    }

    return keys.every(key => {
        if (!obj) {
            return false;
        }

        obj = obj[key];
        return true;
    });
}

(code in playground)

Answer 2

In my previous response, I mentioned that it may not be feasible to achieve what you are looking for.

The code snippet

anObject.aNestedObject.anotherNestedObject

gets executed prior to calling the someLib.isDefined function. This means that if either anObject or aNestedObject do not exist, an exception will be thrown before the function can be utilized.

One workaround could be passing the expression as a string, like this:

someLib.isDefined("anObject.aNestedObject.anotherNestedObject")

Alternatively, you can perform a check like this:

if (anObject && anObject.aNestedObject && anObject.aNestedObject.anotherNestedObject) {
    // do something
}

Another option is to create your own function, which is quite straightforward:

function exists(obj: any, keys: string | string[]) {
    if (typeof keys === "string") {
        keys = keys.split(".");
    }

    return keys.every(key => {
        if (!obj) {
            return false;
        }

        obj = obj[key];
        return true;
    });
}

(code in playground)

Answer 3

Answer №2

Understanding Lodash's has() method:

_.has(object, path)

For instance:

var object = {a: {b: 'example', c: 'demo'}};
_.has(object, 'a.b');
// => true
_.has(object, 'a.d');
// => false

Detailed guide
Check out the source code for _.has()

Answer 4

Understanding Lodash's has() method:

_.has(object, path)

For instance:

var object = {a: {b: 'example', c: 'demo'}};
_.has(object, 'a.b');
// => true
_.has(object, 'a.d');
// => false

Detailed guide
Check out the source code for _.has()

Answer 5

Answer №3

There isn't a widely recognized function for accomplishing this task, but you can verify it securely using the following method:

if (typeof anObject !== "undefined"  
&& typeof anObject.aNestedObject !== "undefined" 
&& typeof anObject.aNestedObject.anotherNestedObject !== "undefined") {
   console.log("defined");
}else{
  console.log("undefined");
}

Answer 6

There isn't a widely recognized function for accomplishing this task, but you can verify it securely using the following method:

if (typeof anObject !== "undefined"  
&& typeof anObject.aNestedObject !== "undefined" 
&& typeof anObject.aNestedObject.anotherNestedObject !== "undefined") {
   console.log("defined");
}else{
  console.log("undefined");
}

A comprehensive method in JavaScript to determine if a variable is defined

Answer №1

Answer №2

Answer №3

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